netlink: specs: allow header properties for attribute sets

rt-link has a number of disjoint headers, plus it uses attributes
of other families (e.g. DPLL). Allow declaring a attribute set
as "foreign" by specifying which header its definition is coming
from.

Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20250418021706.1967583-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/netlink/genetlink-c.yaml

@@ -148,6 +148,9 @@ properties:
         attr-max-name:
           description: The explicit name for last member of attribute enum.
           type: string
+        header:
+          description: For C-compatible languages, header which already defines this attribute set.
+          type: string
         # End genetlink-c
         attributes:
           description: List of attributes in the space.

Documentation/netlink/genetlink-legacy.yaml

@@ -193,6 +193,9 @@ properties:
         attr-max-name:
           description: The explicit name for last member of attribute enum.
           type: string
+        header:
+          description: For C-compatible languages, header which already defines this attribute set.
+          type: string
         # End genetlink-c
         attributes:
           description: List of attributes in the space.

Documentation/netlink/netlink-raw.yaml

@@ -207,6 +207,9 @@ properties:
         attr-max-name:
           description: The explicit name for last member of attribute enum.
           type: string
+        header:
+          description: For C-compatible languages, header which already defines this attribute set.
+          type: string
         # End genetlink-c
         attributes:
           description: List of attributes in the space.

tools/net/ynl/pyynl/ynl_gen_c.py

@@ -2909,7 +2909,7 @@ def main():
             cw.p(f'#include "{hdr_file}"')
             cw.p('#include "ynl.h"')
         headers = []
-    for definition in parsed['definitions']:
+    for definition in parsed['definitions'] + parsed['attribute-sets']:
         if 'header' in definition:
             headers.append(definition['header'])
     if args.mode == 'user':