net: add inline function skb_csum_is_sctp

This patch is to define a inline function skb_csum_is_sctp(), and
also replace all places where it checks if it's a SCTP CSUM skb.
This function would be used later in many networking drivers in
the following patches.

Suggested-by: Alexander Duyck <alexander.duyck@gmail.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: hongrongxuan <hongrongxuan@huawei.com>

drivers/net/ethernet/pensando/ionic/ionic_txrx.c

@@ -740,7 +740,7 @@ static int ionic_tx_calc_csum(struct ionic_queue *q, struct sk_buff *skb)
 	desc->csum_start = cpu_to_le16(skb_checksum_start_offset(skb));
 	desc->csum_offset = cpu_to_le16(skb->csum_offset);
 
-	if (skb->csum_not_inet)
+	if (skb_csum_is_sctp(skb))
 		stats->crc32_csum++;
 	else
 		stats->csum++;

include/linux/skbuff.h

@@ -4583,5 +4583,10 @@ static inline void skb_reset_redirect(struct sk_buff *skb)
 #endif
 }
 
+static inline bool skb_csum_is_sctp(struct sk_buff *skb)
+{
+	return skb->csum_not_inet;
+}
+
 #endif	/* __KERNEL__ */
 #endif	/* _LINUX_SKBUFF_H */

net/core/dev.c

@@ -3249,7 +3249,7 @@ static struct sk_buff *validate_xmit_vlan(struct sk_buff *skb,
 int skb_csum_hwoffload_help(struct sk_buff *skb,
 			    const netdev_features_t features)
 {
-	if (unlikely(skb->csum_not_inet))
+	if (unlikely(skb_csum_is_sctp(skb)))
 		return !!(features & NETIF_F_SCTP_CRC) ? 0 :
 			skb_crc32c_csum_help(skb);