cxgb4vf: Fix extraction of cpl_rx_pkt from the response queue descriptor

This was preventing GRO and RxCheckSum offload to happen.

Signed-off-by: Jay Hernandez <jay@chelsio.com>
Signed-off-by: Vipul Pandya <vipul@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>