[IPV6]: fix implicit declaration of function `xfrm6_tunnel_unregister'

Signed-off-by: NCal Peake <cp@absolutedigital.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/ip6_tunnel.c

@@ -1123,7 +1123,7 @@ static inline int ip6ip6_register(void)
 
 static inline int ip6ip6_unregister(void)
 {
-	return xfrm6_tunnel_unregister(&ip6ip6_handler);
+	return xfrm6_tunnel_deregister(&ip6ip6_handler);
 }
 #else
 static struct inet6_protocol xfrm6_tunnel_protocol = {