pch_gbe: reprogram multicast address register on reset

The reset logic after a Rx FIFO overrun will clear the programmed
multicast addresses. This patch fixes the issue by reprogramming the
registers after the reset.

[ RC - Rebased Takahiro's changes and wrote a commit message
  explaining the changes. ]

Signed-off-by: Takahiro Shimizu <tshimizu818@gmail.com>
Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>