bridge: Correctly encode addresses when dumping mdb entries

When dumping mdb table, set the addresses the kernel returns
based on the address protocol type.

Signed-off-by: Vlad Yasevich <vyasevic@redhat.com>
Acked-by: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>