bnx2x: Fix Duplex setting for 54618se

BCM54618SE is used to advertise half-duplex even if HD was not requested by the
user. This change makes the legacy speed/duplex advertisement for this PHY
exactly according to the requested speed and duplex.

Signed-off-by: Yaniv Rosner <yanivr@broadcom.com>
Signed-off-by: Ariel Elior <ariele@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>