staging: r8188eu: Fix PPPoE tag insertion on big endian systems

In __nat25_add_pppoe_tag(), the tag length is read from the tag data structure. The value is kept in network format, but read as raw value. With -Warray-bounds, this results in the following gcc error/warning when building the driver on a big endian system such as alpha.

In function '__nat25_add_pppoe_tag',
inlined from 'nat25_db_handle' at
drivers/staging/r8188eu/core/rtw_br_ext.c:479:11:
arch/alpha/include/asm/string.h:22:16: error:

	'__builtin_memcpy' forming offset [40, 2051] is out of the bounds
	[0, 40] of object 'tag_buf' with type 'unsigned char[40]'

Add the missing be16_to_cpu() to fix the compile error. It should be noted, however, that this fix means that the code did probably not work on little endian systems and/or that the driver has other endiannes related issues. A build with C=1 suggests that this is indeed the case. This patch does not attempt to fix any of those issues.

---
v2: Use be16_to_cpu().
Add comment to patch description suggesting that the driver may have other endianness related problems.

 drivers/staging/r8188eu/core/rtw_br_ext.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index d68611ef22f8..f056204c0fdb 100644
@@ -70,7 +70,7 @@ static int __nat25_add_pppoe_tag(struct sk_buff *skb, struct pppoe_tag *tag)
 	struct pppoe_hdr *ph = (struct pppoe_hdr *)(skb->data + ETH_HLEN);
 	int data_len;
 
-	data_len = tag->tag_len + TAG_HDR_LEN;
+	data_len = be16_to_cpu(tag->tag_len) + TAG_HDR_LEN;
 	if (skb_tailroom(skb) < data_len)
 		return -1;
 

2.35.1