ipv6: set skb->protocol on tcp, raw and ip6_append_data genereated skbs

Currently we don't initialize skb->protocol when transmitting data via
tcp, raw(with and without inclhdr) or udp+ufo or appending data directly
to the socket transmit queue (via ip6_append_data). This needs to be
done so that we can get the correct mtu in the xfrm layer.

Setting of skb->protocol happens only in functions where we also have
a transmitting socket and a new skb, so we don't overwrite old values.

Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index c45f7a5..cdaed47 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -628,6 +628,7 @@
 		goto error;
 	skb_reserve(skb, hlen);
 
+	skb->protocol = htons(ETH_P_IPV6);
 	skb->priority = sk->sk_priority;
 	skb->mark = sk->sk_mark;
 	skb_dst_set(skb, &rt->dst);