bridge: fdb: Fix filtering with strict checking disabled

bridge: fdb: Fix filtering with strict checking disabled

Older kernels expect an ifinfomsg struct as the ancillary header, and
after kernel commit bd961c9bc664 ("rtnetlink: fix rtnl_fdb_dump() for ndmsg
header") can handle either ifinfomsg or ndmsg. Strict data checking only
allows ndmsg.

Use the new RTNL_HANDLE_F_STRICT_CHK flag to know which header to send.

Signed-off-by: David Ahern <dsahern@gmail.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Tested-by: Ido Schimmel <idosch@mellanox.com>