doc/netlink: Add spec for rt addr messages

Add schema for rt addr with support for:
     - newaddr, deladdr, getaddr (dump)
Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20230825122756.7603-11-donald.hunter@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/netlink/specs/rt_addr.yaml

+# SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause)
+
+name: rt-addr
+protocol: netlink-raw
+protonum: 0
+
+doc:
+  Address configuration over rtnetlink.
+
+definitions:
+  -
+    name: ifaddrmsg
+    type: struct
+    members:
+      -
+        name: ifa-family
+        type: u8
+      -
+        name: ifa-prefixlen
+        type: u8
+      -
+        name: ifa-flags
+        type: u8
+        enum: ifa-flags
+        enum-as-flags: true
+      -
+        name: ifa-scope
+        type: u8
+      -
+        name: ifa-index
+        type: u32
+  -
+    name: ifa-cacheinfo
+    type: struct
+    members:
+      -
+        name: ifa-prefered
+        type: u32
+      -
+        name: ifa-valid
+        type: u32
+      -
+        name: cstamp
+        type: u32
+      -
+        name: tstamp
+        type: u32
+
+  -
+    name: ifa-flags
+    type: flags
+    entries:
+      -
+        name: secondary
+      -
+        name: nodad
+      -
+        name: optimistic
+      -
+        name: dadfailed
+      -
+        name: homeaddress
+      -
+        name: deprecated
+      -
+        name: tentative
+      -
+        name: permanent
+      -
+        name: managetempaddr
+      -
+        name: noprefixroute
+      -
+        name: mcautojoin
+      -
+        name: stable-privacy
+
+attribute-sets:
+  -
+    name: addr-attrs
+    attributes:
+      -
+        name: ifa-address
+        type: binary
+        display-hint: ipv4
+      -
+        name: ifa-local
+        type: binary
+        display-hint: ipv4
+      -
+        name: ifa-label
+        type: string
+      -
+        name: ifa-broadcast
+        type: binary
+        display-hint: ipv4
+      -
+        name: ifa-anycast
+        type: binary
+      -
+        name: ifa-cacheinfo
+        type: binary
+        struct: ifa-cacheinfo
+      -
+        name: ifa-multicast
+        type: binary
+      -
+        name: ifa-flags
+        type: u32
+        enum: ifa-flags
+        enum-as-flags: true
+      -
+        name: ifa-rt-priority
+        type: u32
+      -
+        name: ifa-target-netnsid
+        type: binary
+      -
+        name: ifa-proto
+        type: u8
+
+
+operations:
+  fixed-header: ifaddrmsg
+  enum-model: directional
+  list:
+    -
+      name: newaddr
+      doc: Add new address
+      attribute-set: addr-attrs
+      do:
+        request:
+          value: 20
+          attributes: &ifaddr-all
+            - ifa-family
+            - ifa-flags
+            - ifa-prefixlen
+            - ifa-scope
+            - ifa-index
+            - ifa-address
+            - ifa-label
+            - ifa-local
+            - ifa-cacheinfo
+    -
+      name: deladdr
+      doc: Remove address
+      attribute-set: addr-attrs
+      do:
+        request:
+          value: 21
+          attributes:
+            - ifa-family
+            - ifa-flags
+            - ifa-prefixlen
+            - ifa-scope
+            - ifa-index
+            - ifa-address
+            - ifa-local
+    -
+      name: getaddr
+      doc: Dump address information.
+      attribute-set: addr-attrs
+      dump:
+        request:
+          value: 22
+          attributes:
+            - ifa-index
+        reply:
+          value: 20
+          attributes: *ifaddr-all
+
+mcast-groups:
+  list:
+    -
+      name: rtnlgrp-ipv4-ifaddr
+      value: 5
+    -
+      name: rtnlgrp-ipv6-ifaddr
+      value: 9