bonding: reset master mac on first enslave failure

If the bond device is supposed to get the first slave's MAC address and
the first enslavement fails then we need to reset the master's MAC
otherwise it will stay the same as the failed slave device. We do it
after err_undo_flags since that is the first place where the MAC can be
changed and we check if it should've been the first slave and if the
bond's MAC was set to it because that err place is used by multiple
locations prior to changing the master's MAC address.

Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>