bnx2x: Allow RX/TX pause control in autoneg

Currently, when link is configured to auto-negotiate the flow control,
disabling RX/TX pause via ethtool doesn't work.

This fixes the behaviour, advertising asymmetric pause in case either one
is exclusively enabled.

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