bnx2: Refine remote PHY locking.

bnx2_set_remote_link() should be called under bp->phy_lock to protect
against concurrent polling and interrupt calls.  This change is needed
by the next patch which will add one initial poll of the remote PHY
link status.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: Benjamin Li <benli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>