net: add basic C code generators for Netlink

Code generators to turn Netlink specs into C code.
I'm definitely not proud of it.

The main generator is in Python, there's a bash script
to regen all code-gen'ed files in tree after making
spec changes.
Acked-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

MAINTAINERS

@@ -14577,6 +14577,7 @@ F:	include/uapi/linux/netdevice.h
 F:	lib/net_utils.c
 F:	lib/random32.c
 F:	net/
+F:	tools/net/
 F:	tools/testing/selftests/net/
 
 NETWORKING [IPSEC]

tools/net/ynl/ynl-regen.sh

+#!/bin/bash
+# SPDX-License-Identifier: BSD-3-Clause
+
+TOOL=$(dirname $(realpath $0))/ynl-gen-c.py
+
+force=
+
+while [ ! -z "$1" ]; do
+  case "$1" in
+    -f ) force=yes; shift ;;
+    * )  echo "Unrecognized option '$1'"; exit 1 ;;
+  esac
+done
+
+KDIR=$(dirname $(dirname $(dirname $(dirname $(realpath $0)))))
+
+files=$(git grep --files-with-matches '^/\* YNL-GEN \(kernel\|uapi\)')
+for f in $files; do
+    # params:     0       1      2     3
+    #         $YAML YNL-GEN kernel $mode
+    params=( $(git grep -B1 -h '/\* YNL-GEN' $f | sed 's@/\*\(.*\)\*/@\1@') )
+
+    if [ $f -nt ${params[0]} -a -z "$force" ]; then
+	echo -e "\tSKIP $f"
+	continue
+    fi
+
+    echo -e "\tGEN ${params[2]}\t$f"
+    $TOOL --mode ${params[2]} --${params[3]} --spec $KDIR/${params[0]} -o $f
+done