[BNX2]: Fix UDP checksum verification

Fix TCP/UDP checksum verification. Use status bits in the buffer
descriptor instead of the checksum value to verify rx checksum.
Using the checksum value will be incorrect if the UDP packet has
zero in the UDP checksum field.

Firmware update required for this fix.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>