ipv6: honor IPV6_PKTINFO with v4 mapped addresses on sendmsg

In case we decide in udp6_sendmsg to send the packet down the ipv4
udp_sendmsg path because the destination is either of family AF_INET or
the destination is an ipv4 mapped ipv6 address, we don't honor the
maybe specified ipv4 mapped ipv6 address in IPV6_PKTINFO.

We simply can check for this option in ip_cmsg_send because no calls to
ipv6 module functions are needed to do so.

Reported-by: Gert Doering <gert@space.net>
Cc: Tore Anderson <tore@fud.no>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
index 2d11c09..f4b19e5 100644
--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c
@@ -727,7 +727,7 @@
 	sock_tx_timestamp(sk, &ipc.tx_flags);
 
 	if (msg->msg_controllen) {
-		err = ip_cmsg_send(sock_net(sk), msg, &ipc);
+		err = ip_cmsg_send(sock_net(sk), msg, &ipc, false);
 		if (err)
 			return err;
 		if (ipc.opt)