bnx2x: Fix BCM54618se invalid link indication

After resetting BCM54618se, link partner would still see link since the PHY wasn't put into low-power state.

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>