docs: networking: convert seg6-sysctl.txt to ReST

- add SPDX header;
- mark code blocks and literals as such;
- add a document title;
- adjust chapters, adding proper markups;
- mark lists as such;
- 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

@@ -102,6 +102,7 @@ Contents:
    rxrpc
    sctp
    secid
+   seg6-sysctl
 
 .. only::  subproject and html
 

Documentation/networking/seg6-sysctl.txt → Documentation/networking/seg6-sysctl.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+====================
+Seg6 Sysfs variables
+====================
+
+
 /proc/sys/net/conf/<iface>/seg6_* variables:
+============================================
 
 seg6_enabled - BOOL
 	Accept or drop SR-enabled IPv6 packets on this interface.
 
 	Relevant packets are those with SRH present and DA = local.
 
-	0 - disabled (default)
-	not 0 - enabled
+	* 0 - disabled (default)
+	* not 0 - enabled
 
 seg6_require_hmac - INTEGER
 	Define HMAC policy for ingress SR-enabled packets on this interface.
 
-	-1 - Ignore HMAC field
-	0 - Accept SR packets without HMAC, validate SR packets with HMAC
-	1 - Drop SR packets without HMAC, validate SR packets with HMAC
+	* -1 - Ignore HMAC field
+	* 0 - Accept SR packets without HMAC, validate SR packets with HMAC
+	* 1 - Drop SR packets without HMAC, validate SR packets with HMAC
 
 	Default is 0.