6lowpan: fix tag variable size

Function lowpan_alloc_new_frame() takes u8 tag as an argument. However,
its only caller, lowpan_process_data() passes down a u16. Hence,
the tag value can get corrupted. This prevent 6lowpan fragment reassembly of a
message when the fragment tag value is over 256.

Signed-off-by: Alexander Smirnov <alex.bluesman.smirnov@gmail.com>
Cc: Tony Cheneau <tony.cheneau@amnesiak.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ieee802154/6lowpan.c

@@ -646,7 +646,7 @@ static void lowpan_fragment_timer_expired(unsigned long entry_addr)
 }
 
 static struct lowpan_fragment *
-lowpan_alloc_new_frame(struct sk_buff *skb, u8 iphc0, u8 len, u8 tag)
+lowpan_alloc_new_frame(struct sk_buff *skb, u8 iphc0, u8 len, u16 tag)
 {
 	struct lowpan_fragment *frame;