ipv4: Add a socket release callback for datagram sockets

This implements a socket release callback function to check
if the socket cached route got invalid during the time
we owned the socket. The function is used from udp, raw
and ping sockets.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/ip.h b/include/net/ip.h
index 0707fb9..a68f838 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -143,6 +143,8 @@
 extern int		ip4_datagram_connect(struct sock *sk, 
 					     struct sockaddr *uaddr, int addr_len);
 
+extern void ip4_datagram_release_cb(struct sock *sk);
+
 struct ip_reply_arg {
 	struct kvec iov[1];   
 	int	    flags;