ipv4: fix ip_send_skb()

ip_send_skb() can send orphaned skb, so we must pass the net pointer to
avoid possible NULL dereference in error path.

Bug added by commit 3a7c384ffd57 (ipv4: tcp: unicast_sock should not
land outside of TCP stack)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index b4c3582..6f6d1ac 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -758,7 +758,7 @@
 		uh->check = CSUM_MANGLED_0;
 
 send:
-	err = ip_send_skb(skb);
+	err = ip_send_skb(sock_net(sk), skb);
 	if (err) {
 		if (err == -ENOBUFS && !inet->recverr) {
 			UDP_INC_STATS_USER(sock_net(sk),