net: change proto destroy method to return void

Change struct proto destroy function pointer to return void.  Noticed
by Al Viro.

Signed-off-by: Brian Haley <brian.haley@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index e0693ff..09687f7 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -879,15 +879,13 @@
 	goto out;
 }
 
-int udpv6_destroy_sock(struct sock *sk)
+void udpv6_destroy_sock(struct sock *sk)
 {
 	lock_sock(sk);
 	udp_v6_flush_pending_frames(sk);
 	release_sock(sk);
 
 	inet6_destroy_sock(sk);
-
-	return 0;
 }
 
 /*