bnx2x: PFC fix

Fix a problem in which PFC frames are not honored, due to incorrect link
attributes synchronization following PMF migration, and verify PFC XON is not
stuck from previous link change.

Signed-off-by: Yaniv Rosner <yanivr@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>