bonding: correctly update link status during mii-commit phase

bond_miimon_commit() marks the link UP after attempting to get the speed
and duplex settings for the link. There is a possibility that
bond_update_speed_duplex() could fail. This is another place where it
could result into an inconsistent bonding link state.

With this patch the link will be marked UP only if the speed and duplex
values retrieved have sane values and processed further.

Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>