vsock: Allow retrying on connect() failure

sk_err is set when a (connectible) connect() fails. Effectively, this makes
an otherwise still healthy SS_UNCONNECTED socket impossible to use for any
subsequent connection attempts.

Clear sk_err upon trying to establish a connection.

Fixes: d021c34 ("VSOCK: Introduce VM Sockets")
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Luigi Leonardi <leonardi@redhat.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Link: https://patch.msgid.link/20250128-vsock-transport-vs-autobind-v3-2-1cf57065b770@rbox.co
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: mmhal

net/vmw_vsock/af_vsock.c

@@ -1523,6 +1523,11 @@ static int vsock_connect(struct socket *sock, struct sockaddr *addr,
 		if (err < 0)
 			goto out;
 
+		/* sk_err might have been set as a result of an earlier
+		 * (failed) connect attempt.
+		 */
+		sk->sk_err = 0;
+
 		/* Mark sock as connecting and set the error code to in
 		 * progress in case this is a non-blocking connect.
 		 */