6lowpan: Fix fragmentation with link-local compressed addresses

When a new 6lowpan fragment is received, a skbuff is allocated for
the reassembled packet. However when a 6lowpan packet compresses
link-local addresses based on link-layer addresses, the processing
function relies on the skb mac control block to find the related
link-layer address.

This patch copies the control block from the first fragment into
the newly allocated skb to keep a trace of the link-layer addresses
in case of a link-local compressed address.

Edit: small changes on comment issue
Signed-off-by: David Hauweele <david@hauweele.net>
Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Reviewed-by: Werner Almesberger <werner@almesberger.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ieee802154/6lowpan.c

@@ -698,6 +698,12 @@ lowpan_alloc_new_frame(struct sk_buff *skb, u16 len, u16 tag)
 	skb_reserve(frame->skb, sizeof(struct ipv6hdr));
 	skb_put(frame->skb, frame->length);
 
+	/* copy the first control block to keep a
+	 * trace of the link-layer addresses in case
+	 * of a link-local compressed address
+	 */
+	memcpy(frame->skb->cb, skb->cb, sizeof(skb->cb));
+
 	init_timer(&frame->timer);
 	/* time out is the same as for ipv6 - 60 sec */
 	frame->timer.expires = jiffies + LOWPAN_FRAG_TIMEOUT;