net: igc: 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 igc 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/igc/igc_main.c

@@ -949,15 +949,6 @@ static void igc_tx_ctxtdesc(struct igc_ring *tx_ring,
 	}
 }
 
-static inline bool igc_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 igc_tx_csum(struct igc_ring *tx_ring, struct igc_tx_buffer *first)
 {
 	struct sk_buff *skb = first->skb;
@@ -980,10 +971,7 @@ static void igc_tx_csum(struct igc_ring *tx_ring, struct igc_tx_buffer *first)
 		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) &&
-		     igc_ipv6_csum_is_sctp(skb))) {
+		if (skb_csum_is_sctp(skb)) {
 			type_tucmd = IGC_ADVTXD_TUCMD_L4T_SCTP;
 			break;
 		}