bonding: move dev_addr cpy to bond_enslave

Move the code that copies slave's mac address in case that's the first slave into
bond_enslave. Ifenslave app does this also but that's not a problem. This is
something that should be done in bond_enslave, and it shound not matter from
where is it called.

Signed-off-by: Jiri Pirko <jpirko@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>