net: ixgbe: use skb_csum_is_sctp instead of protocol check

Using skb_csum_is_sctp is a easier way to validate it's a SCTP CRC
checksum offload packet, and yet it also makes ixgbe support SCTP
CRC checksum offload for UDP and GRE encapped packets, just as it
does in igb driver.
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -8039,15 +8039,6 @@ static int ixgbe_tso(struct ixgbe_ring *tx_ring,
 	return 1;
 }
 
-static inline bool ixgbe_ipv6_csum_is_sctp(struct sk_buff *skb)
-{
-	unsigned int offset = 0;
-
-	ipv6_find_hdr(skb, &offset, IPPROTO_SCTP, NULL, NULL);
-
-	return offset == skb_checksum_start_offset(skb);
-}
-
 static void ixgbe_tx_csum(struct ixgbe_ring *tx_ring,
 			  struct ixgbe_tx_buffer *first,
 			  struct ixgbe_ipsec_tx_data *itd)
@@ -8073,10 +8064,7 @@ static void ixgbe_tx_csum(struct ixgbe_ring *tx_ring,
 		break;
 	case offsetof(struct sctphdr, checksum):
 		/* validate that this is actually an SCTP request */
-		if (((first->protocol == htons(ETH_P_IP)) &&
-		     (ip_hdr(skb)->protocol == IPPROTO_SCTP)) ||
-		    ((first->protocol == htons(ETH_P_IPV6)) &&
-		     ixgbe_ipv6_csum_is_sctp(skb))) {
+		if (skb_csum_is_sctp(skb)) {
 			type_tucmd = IXGBE_ADVTXD_TUCMD_L4T_SCTP;
 			break;
 		}