SUNRPC: Fix Oops in xs_tcp_send_request() when transport is disconnected

If a disconnection occurs while we're trying to reply to a server
callback, then we may end up calling xs_tcp_send_request() with a NULL
value for transport->inet, which trips up the call to
tcp_sock_set_cork().

Fixes: d737e5d418 ("SUNRPC: Set TCP_CORK until the transmit queue is empty")
Cc: stable@vger.kernel.org
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

net/sunrpc/xprtsock.c

@@ -1010,6 +1010,8 @@ static int xs_tcp_send_request(struct rpc_rqst *req)
 			kernel_sock_shutdown(transport->sock, SHUT_RDWR);
 		return -ENOTCONN;
 	}
+	if (!transport->inet)
+		return -ENOTCONN;
 
 	xs_pktdump("packet data:",
 				req->rq_svec->iov_base,