gk: fix checksum issue

Some examples that implement the RFC1624 [Eqn. 4] use the network order:
https://elixir.bootlin.com/linux/latest/source/net/ipv4/netfilter/ipt_ECN.c#L38

This patch removes the byte-order convertion for checksum.

gk/bpf.c

@@ -167,19 +167,19 @@ update_pkt_priority(struct ipacket *packet, int priority,
 
 	if (packet->flow.proto == RTE_ETHER_TYPE_IPV4) {
 		struct rte_ipv4_hdr *ip4hdr = packet->l3_hdr;
-		uint16_t old_val = ntohs(*(uint16_t *)ip4hdr);
+		uint16_t old_val = *(uint16_t *)ip4hdr;
 		uint16_t new_val;
 
 		mask = (1 << 2) - 1;
 
 		ip4hdr->type_of_service = (priority << 2) |
 			(ip4hdr->type_of_service & mask);
 
-		new_val = ntohs(*(uint16_t *)ip4hdr);
+		new_val = *(uint16_t *)ip4hdr;
 
 		/* According to RFC1624 [Eqn. 4]. */
-		ip4hdr->hdr_checksum = htons(ntohs(ip4hdr->hdr_checksum) -
-			~old_val - new_val);
+		ip4hdr->hdr_checksum = ip4hdr->hdr_checksum -
+			~old_val - new_val;
 	} else if (likely(packet->flow.proto == RTE_ETHER_TYPE_IPV6)) {
 		struct rte_ipv6_hdr *ip6hdr = packet->l3_hdr;