net: libwx: fix Tx L4 checksum

The hardware only supports L4 checksum offload for TCP/UDP/SCTP protocol.
There was a bug to set Tx checksum flag for the other protocol that results
in Tx ring hang. Fix to compute software checksum for these packets.

Fixes: 3403960 ("net: wangxun: libwx add tx offload functions")
Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>
Link: https://patch.msgid.link/20250324103235.823096-2-jiawenwu@trustnetic.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/wangxun/libwx/wx_lib.c

@@ -1337,6 +1337,7 @@ static void wx_tx_csum(struct wx_ring *tx_ring, struct wx_tx_buffer *first,
 	u8 tun_prot = 0;
 
 	if (skb->ip_summed != CHECKSUM_PARTIAL) {
+csum_failed:
 		if (!(first->tx_flags & WX_TX_FLAGS_HW_VLAN) &&
 		    !(first->tx_flags & WX_TX_FLAGS_CC))
 			return;
@@ -1441,7 +1442,8 @@ static void wx_tx_csum(struct wx_ring *tx_ring, struct wx_tx_buffer *first,
 					WX_TXD_L4LEN_SHIFT;
 			break;
 		default:
-			break;
+			skb_checksum_help(skb);
+			goto csum_failed;
 		}
 
 		/* update TX checksum flag */