llc: Return -EINPROGRESS from llc_ui_connect()

Given a zero sk_sndtimeo, llc_ui_connect() skips waiting for state
change and returns 0, confusing userspace applications that will assume
the socket is connected, making e.g. getpeername() calls error out.

More specifically, the issue was discovered in libcoap, where
newly-added AF_LLC socket support was behaving differently from AF_INET
connections due to EINPROGRESS handling being skipped.

Set rc to -EINPROGRESS if connect() would not block, akin to AF_INET
sockets.

Signed-off-by: Ernestas Kulik <ernestas.k@iconn-networks.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260421060304.285419-1-ernestas.k@iconn-networks.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: ernestask

net/llc/af_llc.c

@@ -520,8 +520,10 @@ static int llc_ui_connect(struct socket *sock, struct sockaddr_unsized *uaddr,
 	if (sk->sk_state == TCP_SYN_SENT) {
 		const long timeo = sock_sndtimeo(sk, flags & O_NONBLOCK);
 
-		if (!timeo || !llc_ui_wait_for_conn(sk, timeo))
+		if (!timeo || !llc_ui_wait_for_conn(sk, timeo)) {
+			rc = -EINPROGRESS;
 			goto out;
+		}
 
 		rc = sock_intr_errno(timeo);
 		if (signal_pending(current))