tcp: add tcp_sock_set_keepintvl

Add a helper to directly set the TCP_KEEPINTVL sockopt from kernel space
without going through a fake uaccess.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/rds/tcp_listen.c

@@ -53,12 +53,10 @@ int rds_tcp_keepalive(struct socket *sock)
 		goto bail;
 
 	tcp_sock_set_keepidle(sock->sk, keepidle);
-
 	/* KEEPINTVL is the interval between successive probes. We follow
 	 * the model in xs_tcp_finish_connecting() and re-use keepidle.
 	 */
-	ret = kernel_setsockopt(sock, IPPROTO_TCP, TCP_KEEPINTVL,
-				(char *)&keepidle, sizeof(keepidle));
+	tcp_sock_set_keepintvl(sock->sk, keepidle);
 bail:
 	return ret;
 }