staging: wilc1000: Use common structs to parse ip packets

Use structs ethhdr, iphdr and tcphdr instead of manual parsing in
tcp_process.
This commit fix handling of ip packets containing options.
It also fixes the following sparse warning:

drivers/staging/wilc1000//wilc_wlan.c:201:19: warning: cast to restricted __be16
Signed-off-by: Thibaut Robert <thibaut.robert@gmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wilc1000/wilc_wlan.c

 // SPDX-License-Identifier: GPL-2.0
+#include <linux/if_ether.h>
+#include <linux/ip.h>
 #include "wilc_wfi_netdevice.h"
 #include "wilc_wlan_cfg.h"
 
@@ -150,9 +152,8 @@ static inline int add_tcp_pending_ack(u32 ack, u32 session_index,
 
 static inline void tcp_process(struct net_device *dev, struct txq_entry_t *tqe)
 {
-	u8 *eth_hdr_ptr;
-	u8 *buffer = tqe->buffer;
-	unsigned short h_proto;
+	void *buffer = tqe->buffer;
+	const struct ethhdr *eth_hdr_ptr = buffer;
 	int i;
 	unsigned long flags;
 	struct wilc_vif *vif;
@@ -163,37 +164,23 @@ static inline void tcp_process(struct net_device *dev, struct txq_entry_t *tqe)
 
 	spin_lock_irqsave(&wilc->txq_spinlock, flags);
 
-	eth_hdr_ptr = &buffer[0];
-	h_proto = ntohs(*((unsigned short *)&eth_hdr_ptr[12]));
-	if (h_proto == ETH_P_IP) {
-		u8 *ip_hdr_ptr;
-		u8 protocol;
+	if (eth_hdr_ptr->h_proto == htons(ETH_P_IP)) {
+		const struct iphdr *ip_hdr_ptr = buffer + ETH_HLEN;
 
-		ip_hdr_ptr = &buffer[ETHERNET_HDR_LEN];
-		protocol = ip_hdr_ptr[9];
-
-		if (protocol == 0x06) {
-			u8 *tcp_hdr_ptr;
+		if (ip_hdr_ptr->protocol == IPPROTO_TCP) {
+			const struct tcphdr *tcp_hdr_ptr;
 			u32 IHL, total_length, data_offset;
 
-			tcp_hdr_ptr = &ip_hdr_ptr[IP_HDR_LEN];
-			IHL = (ip_hdr_ptr[0] & 0xf) << 2;
-			total_length = ((u32)ip_hdr_ptr[2] << 8) +
-					(u32)ip_hdr_ptr[3];
-			data_offset = ((u32)tcp_hdr_ptr[12] & 0xf0) >> 2;
+			IHL = ip_hdr_ptr->ihl << 2;
+			tcp_hdr_ptr = buffer + ETH_HLEN + IHL;
+			total_length = ntohs(ip_hdr_ptr->tot_len);
+
+			data_offset = tcp_hdr_ptr->doff << 2;
 			if (total_length == (IHL + data_offset)) {
 				u32 seq_no, ack_no;
 
-				seq_no = ((u32)tcp_hdr_ptr[4] << 24) +
-					 ((u32)tcp_hdr_ptr[5] << 16) +
-					 ((u32)tcp_hdr_ptr[6] << 8) +
-					 (u32)tcp_hdr_ptr[7];
-
-				ack_no = ((u32)tcp_hdr_ptr[8] << 24) +
-					 ((u32)tcp_hdr_ptr[9] << 16) +
-					 ((u32)tcp_hdr_ptr[10] << 8) +
-					 (u32)tcp_hdr_ptr[11];
-
+				seq_no = ntohl(tcp_hdr_ptr->seq);
+				ack_no = ntohl(tcp_hdr_ptr->ack_seq);
 				for (i = 0; i < tcp_session; i++) {
 					u32 j = ack_session_info[i].seq_num;