When a client mux (h2/h3) connection goes idle between transactions it sits in
LRS_IDLING.  On reusing it for a new stream, lws_vhost_active_conns() adopts
the new stream directly onto the network wsi but left it in LRS_IDLING.

LRS_IDLING does not carry LWSIFS_POCB, so lwsi_state_can_handle_POLLOUT() is
false for it and the network wsi's POLLOUT is never serviced: the child-walking
POLLOUT loop never runs, the new stream's HEADERS are never sent
(lws_h2_client_handshake() is never reached), and its response is never read.
The request just hangs.

Put the revived connection back into LRS_ESTABLISHED (the state it uses while
actively muxing) and clear the keep-warm idle timeout, so its POLLOUT is
serviced and the queued stream's headers go out.  Same fix for the h3/quic
branch.