docs: networking: convert netif-msg.txt to ReST

- add SPDX header;
- adjust title and chapter markups;
- mark lists as such;
- mark code blocks and literals as such;
- adjust identation, whitespaces and blank lines;
- add to networking/index.rst.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/index.rst

@@ -84,6 +84,7 @@ Contents:
    netdev-features
    netdevices
    netfilter-sysctl
+   netif-msg
 
 .. only::  subproject and html
 

Documentation/networking/netif-msg.txt → Documentation/networking/netif-msg.rst

+.. SPDX-License-Identifier: GPL-2.0
 
-________________
+===============
 NETIF Msg Level
+===============
 
 The design of the network interface message level setting.
 
 History
+-------
 
  The design of the debugging message interface was guided and
  constrained by backwards compatibility previous practice.  It is useful
@@ -18,14 +21,15 @@ History
  The message level was not precisely defined past level 3, but were
  always implemented within +-1 of the specified level.  Drivers tended
  to shed the more verbose level messages as they matured.
-    0  Minimal messages, only essential information on fatal errors.
-    1  Standard messages, initialization status.  No run-time messages
-    2  Special media selection messages, generally timer-driver.
-    3  Interface starts and stops, including normal status messages
-    4  Tx and Rx frame error messages, and abnormal driver operation
-    5  Tx packet queue information, interrupt events.
-    6  Status on each completed Tx packet and received Rx packets
-    7  Initial contents of Tx and Rx packets
+
+   - 0  Minimal messages, only essential information on fatal errors.
+   - 1  Standard messages, initialization status.  No run-time messages
+   - 2  Special media selection messages, generally timer-driver.
+   - 3  Interface starts and stops, including normal status messages
+   - 4  Tx and Rx frame error messages, and abnormal driver operation
+   - 5  Tx packet queue information, interrupt events.
+   - 6  Status on each completed Tx packet and received Rx packets
+   - 7  Initial contents of Tx and Rx packets
 
  Initially this message level variable was uniquely named in each driver
  e.g. "lance_debug", so that a kernel symbolic debugger could locate and
@@ -36,44 +40,56 @@ History
  This approach worked well.  However there is always a demand for
  additional features.  Over the years the following emerged as
  reasonable and easily implemented enhancements
-   Using an ioctl() call to modify the level.
-   Per-interface rather than per-driver message level setting.
-   More selective control over the type of messages emitted.
+
+   - Using an ioctl() call to modify the level.
+   - Per-interface rather than per-driver message level setting.
+   - More selective control over the type of messages emitted.
 
  The netif_msg recommendation adds these features with only a minor
  complexity and code size increase.
 
  The recommendation is the following points
-    Retaining the per-driver integer variable "debug" as a module
+
+  - Retaining the per-driver integer variable "debug" as a module
     parameter with a default level of '1'.
 
-    Adding a per-interface private variable named "msg_enable".  The
-    variable is a bit map rather than a level, and is initialized as
+  - Adding a per-interface private variable named "msg_enable".  The
+    variable is a bit map rather than a level, and is initialized as::
+
        1 << debug
-    Or more precisely
-        debug < 0 ? 0 : 1 << min(sizeof(int)-1, debug)
 
-    Messages should changes from
+    Or more precisely::
+
+	debug < 0 ? 0 : 1 << min(sizeof(int)-1, debug)
+
+    Messages should changes from::
+
       if (debug > 1)
-           printk(MSG_DEBUG "%s: ...
-    to
+	   printk(MSG_DEBUG "%s: ...
+
+    to::
+
       if (np->msg_enable & NETIF_MSG_LINK)
-           printk(MSG_DEBUG "%s: ...
+	   printk(MSG_DEBUG "%s: ...
 
 
 The set of message levels is named
-  Old level   Name   Bit position
-    0    NETIF_MSG_DRV		0x0001
-    1    NETIF_MSG_PROBE	0x0002
-    2    NETIF_MSG_LINK		0x0004
-    2    NETIF_MSG_TIMER	0x0004
-    3    NETIF_MSG_IFDOWN	0x0008
-    3    NETIF_MSG_IFUP		0x0008
-    4    NETIF_MSG_RX_ERR	0x0010
-    4    NETIF_MSG_TX_ERR	0x0010
-    5    NETIF_MSG_TX_QUEUED	0x0020
-    5    NETIF_MSG_INTR		0x0020
-    6    NETIF_MSG_TX_DONE	0x0040
-    6    NETIF_MSG_RX_STATUS	0x0040
-    7    NETIF_MSG_PKTDATA	0x0080
 
+
+  =========   ===================	============
+  Old level   Name			Bit position
+  =========   ===================	============
+    0         NETIF_MSG_DRV		0x0001
+    1         NETIF_MSG_PROBE		0x0002
+    2         NETIF_MSG_LINK		0x0004
+    2         NETIF_MSG_TIMER		0x0004
+    3         NETIF_MSG_IFDOWN		0x0008
+    3         NETIF_MSG_IFUP		0x0008
+    4         NETIF_MSG_RX_ERR		0x0010
+    4         NETIF_MSG_TX_ERR		0x0010
+    5         NETIF_MSG_TX_QUEUED	0x0020
+    5         NETIF_MSG_INTR		0x0020
+    6         NETIF_MSG_TX_DONE		0x0040
+    6         NETIF_MSG_RX_STATUS	0x0040
+    7         NETIF_MSG_PKTDATA		0x0080
+  =========   ===================	============