FOU: Fix no return statement warning for !CONFIG_NET_FOU_IP_TUNNELS

net/ipv4/fou.c: In function ‘ip_tunnel_encap_del_fou_ops’:
net/ipv4/fou.c:861:1: warning: no return statement in function returning non-void [-Wreturn-type]

Fixes: a8c5f90f ("ip_tunnel: Ops registration for secondary encap (fou, gue)")
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/fou.c

@@ -856,7 +856,7 @@ static int ip_tunnel_encap_add_fou_ops(void)
 	return 0;
 }
 
-static int ip_tunnel_encap_del_fou_ops(void)
+static void ip_tunnel_encap_del_fou_ops(void)
 {
 }