be2net: Fix error while toggling autoneg of pause parameters

Autonegotiation of pause parameters is possible only on some PHYs.
Ability of autoneg of pause parameters is reported by adapter.
Autoneg of pause parameters cannot be changed from driver.
Fix driver to give error when autoneg mode is toggled by user.

Signed-off-by: Padmanabh Ratnakar <padmanabh.ratnakar@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>