bnx2x: fix rx checksum validation for IPv6

Commit d6cb3e41 "bnx2x: fix checksum validation" caused a performance
regression for IPv6. Rx checksum offload does not work. IPv6 packets
are passed to the stack with CHECKSUM_NONE.

The hardware obviously cannot perform IP checksum validation for IPv6,
because there is no checksum in the IPv6 header. This should not prevent
us from setting CHECKSUM_UNNECESSARY.

Tested on BCM57711.

Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bnx2x/bnx2x_cmn.c

@@ -662,14 +662,16 @@ void bnx2x_csum_validate(struct sk_buff *skb, union eth_rx_cqe *cqe,
 				 struct bnx2x_fastpath *fp,
 				 struct bnx2x_eth_q_stats *qstats)
 {
-	/* Do nothing if no IP/L4 csum validation was done */
-
+	/* Do nothing if no L4 csum validation was done.
+	 * We do not check whether IP csum was validated. For IPv4 we assume
+	 * that if the card got as far as validating the L4 csum, it also
+	 * validated the IP csum. IPv6 has no IP csum.
+	 */
 	if (cqe->fast_path_cqe.status_flags &
-	    (ETH_FAST_PATH_RX_CQE_IP_XSUM_NO_VALIDATION_FLG |
-	     ETH_FAST_PATH_RX_CQE_L4_XSUM_NO_VALIDATION_FLG))
+	    ETH_FAST_PATH_RX_CQE_L4_XSUM_NO_VALIDATION_FLG)
 		return;
 
-	/* If both IP/L4 validation were done, check if an error was found. */
+	/* If L4 validation was done, check if an error was found. */
 
 	if (cqe->fast_path_cqe.type_error_flags &
 	    (ETH_FAST_PATH_RX_CQE_IP_BAD_XSUM_FLG |