net: switchdev: add reminder near struct switchdev_notifier_fdb_info

br_switchdev_fdb_notify() creates an on-stack FDB info variable, and
initializes it member by member. As such, newly added fields which are
not initialized by br_switchdev_fdb_notify() will contain junk bytes
from the stack.

Other uses of struct switchdev_notifier_fdb_info have a struct
initializer which should put zeroes in the uninitialized fields.

Add a reminder above the structure for future developers. Recently
discussed during review.

Link: https://patchwork.kernel.org/project/netdevbpf/patch/20220524152144.40527-2-schultz.hans+netdev@gmail.com/#24877698
Link: https://patchwork.kernel.org/project/netdevbpf/patch/20220524152144.40527-3-schultz.hans+netdev@gmail.com/#24912269
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://lore.kernel.org/r/20220628100831.2899434-1-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/switchdev.h

@@ -239,6 +239,9 @@ struct switchdev_notifier_info {
 	const void *ctx;
 };
 
+/* Remember to update br_switchdev_fdb_populate() when adding
+ * new members to this structure
+ */
 struct switchdev_notifier_fdb_info {
 	struct switchdev_notifier_info info; /* must be first */
 	const unsigned char *addr;