MEDIUM: quic: move conn->qc into conn->handle

MEDIUM: quic: move conn->qc into conn->handle

It was supposed to be there, and probably was not placed there due to
historic limitations in listener_accept(), but now there does not seem
to be a remaining valid reason for keeping the quic_conn out of the
handle. In addition in new_quic_cli_conn() the handle->fd was incorrectly
set to the listener's FD.