bnx2x: Fix self test of BCM57800

Fix the MAC test of the 1G port of the BCM57800 to use the UMAC instead of the XMAC.

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>