bnx2x: Correct asymmetric flow-control

This fixes several issues relating to asymmetric configuration:
 1. When user requests to disable TX, the local-device needs to
    advertise both PAUSE and ASM_DIR, but to avoid transmitting pause
    frames. In the 578xx, it would ignore the TX disable.

 2. When user advertises RX-only, ASM_DIR was advertised instead of
    PAUSE/ASM_DIR.

 3. When changing mode, the advertised PAUSE/ASM_DIR was not cleared
    before setting new one, so disabling RX or TX had no impact on the
    'advertised' as appeared in the 'ethtool -a' output.

Signed-off-by: Yaniv Rosner <Yaniv.Rosner@qlogic.com>
Signed-off-by: Yuval Mintz <Yuval.Mintz@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>