macvlan fdb replace support

Add support for iproute2 command 'bridge fdb replace ...'.
The rtnletlink call back function ndo_fdb_add will be called
with the NLM_F_REPLACE flag set.
Simply return -EOPNOTSUP.

Resubmitted because net-next was closed last week.

Signed-off-by: Thomas Richter <tmricht@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>