bridge: Properly check if local fdb entry can be deleted in br_fdb_delete_by_port

br_fdb_delete_by_port() doesn't care about vlan and mac address of the
bridge device.

As the check is almost the same as mac address changing, slightly modify
fdb_delete_local() and use it.

Note that we can always set added_by_user to 0 in fdb_delete_local() because
- br_fdb_delete_by_port() calls fdb_delete_local() for local entries
  regardless of its added_by_user. In this case, we have to check if another
  port has the same address and vlan, and if found, we have to create the
  entry (by changing dst). This is kernel-added entry, not user-added.
- br_fdb_changeaddr() doesn't call fdb_delete_local() for user-added entry.

Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Acked-by: Vlad Yasevich <vyasevic@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>