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>

net/ipv6/ip6_output.c

@@ -238,6 +238,7 @@ int ip6_xmit(struct sock *sk, struct sk_buff *skb, struct flowi6 *fl6,
 	hdr->saddr = fl6->saddr;
 	hdr->daddr = *first_hop;
 
+	skb->protocol = htons(ETH_P_IPV6);
 	skb->priority = sk->sk_priority;
 	skb->mark = sk->sk_mark;
 
@@ -1057,6 +1058,7 @@ static inline int ip6_ufo_append_data(struct sock *sk,
 		/* initialize protocol header pointer */
 		skb->transport_header = skb->network_header + fragheaderlen;
 
+		skb->protocol = htons(ETH_P_IPV6);
 		skb->ip_summed = CHECKSUM_PARTIAL;
 		skb->csum = 0;
 	}
@@ -1359,6 +1361,7 @@ alloc_new_skb:
 			/*
 			 *	Fill in the control structures
 			 */
+			skb->protocol = htons(ETH_P_IPV6);
 			skb->ip_summed = CHECKSUM_NONE;
 			skb->csum = 0;
 			/* reserve for fragmentation and ipsec header */

net/ipv6/raw.c

@@ -628,6 +628,7 @@ static int rawv6_send_hdrinc(struct sock *sk, void *from, int length,
 		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);