Until now all user mdb entries were added in vlan 0, this patch adds
support to allow the user to specify the vlan for the entry.
About the uapi change a hole in struct br_mdb_entry is used so the size
and offsets are kept the same (verified with pahole and tested with older
iproute2).

Example:
$ bridge mdb
dev br0 port eth1 grp 239.0.0.1 permanent vlan 2000
dev br0 port eth1 grp 239.0.0.1 permanent vlan 200
dev br0 port eth1 grp 239.0.0.1 permanent
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>