ip6_udp_tunnel: Fix checksum calculation

The UDP checksum calculation for VXLAN tunnels is currently using the
socket addresses instead of the actual packet source and destination
addresses.  As a result the checksum calculated is incorrect in some
cases.

Also uh->check was being set twice, first it was set to 0, and then it is
set again in udp6_set_csum.  This change removes the redundant assignment
to 0.

Fixes: acbf74a7 ("vxlan: Refactor vxlan driver to make use of the common UDP tunnel functions.")

Cc: Andy Zhou <azhou@nicira.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6_udp_tunnel.c

@@ -79,15 +79,13 @@ int udp_tunnel6_xmit_skb(struct socket *sock, struct dst_entry *dst,
 	uh->source = src_port;
 
 	uh->len = htons(skb->len);
-	uh->check = 0;
 
 	memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
 	IPCB(skb)->flags &= ~(IPSKB_XFRM_TUNNEL_SIZE | IPSKB_XFRM_TRANSFORMED
 			    | IPSKB_REROUTED);
 	skb_dst_set(skb, dst);
 
-	udp6_set_csum(udp_get_no_check6_tx(sk), skb, &inet6_sk(sk)->saddr,
-		      &sk->sk_v6_daddr, skb->len);
+	udp6_set_csum(udp_get_no_check6_tx(sk), skb, saddr, daddr, skb->len);
 
 	__skb_push(skb, sizeof(*ip6h));
 	skb_reset_network_header(skb);