6lowpan: fix type of datagram size parameter

Datagram size value is u16 because we convert it to host byte order
and we need to read it. Only the tag value belongs to __be16 type.
Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ieee802154/reassembly.c

@@ -35,7 +35,7 @@ static struct inet_frags lowpan_frags;
 static int lowpan_frag_reasm(struct lowpan_frag_queue *fq,
 			     struct sk_buff *prev, struct net_device *dev);
 
-static unsigned int lowpan_hash_frag(__be16 tag, __be16 d_size,
+static unsigned int lowpan_hash_frag(__be16 tag, u16 d_size,
 				     const struct ieee802154_addr *saddr,
 				     const struct ieee802154_addr *daddr)
 {