6lowpan: make lowpan_cb static

CC: Alexander Smirnov <alex.bluesman.smirnov@gmail.com>
Cc: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Cc: linux-zigbee-devel@lists.sourceforge.net
Signed-off-by: NLuis R. Rodriguez <mcgrof@suse.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ieee802154/reassembly.c

@@ -36,7 +36,7 @@ struct lowpan_frag_info {
 	u8 d_offset;
 };
 
-struct lowpan_frag_info *lowpan_cb(struct sk_buff *skb)
+static struct lowpan_frag_info *lowpan_cb(struct sk_buff *skb)
 {
 	return (struct lowpan_frag_info *)skb->cb;
 }