Before this patch the user-specified bridge port was ignored when
deleting an fdb entry and thus one could delete an entry that belonged
to any port.
Example (eth0 and eth1 are br0 ports):
bridge fdb add 00:11:22:33:44:55 dev eth0 master
bridge fdb del 00:11:22:33:44:55 dev eth1 master
(succeeds)

after the patch:
bridge fdb add 00:11:22:33:44:55 dev eth0 master
bridge fdb del 00:11:22:33:44:55 dev eth1 master
RTNETLINK answers: No such file or directory

Based on a patch by Wilson Kok.
Reported-by: Wilson Kok <wkok@cumulusnetworks.com>
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>