In si_connect(), only switch the strema_interface status to SI_ST_RDY if
we're reusing a connection and if the connection's mux is ready. Otherwise,
maybe we're reusing a connection that is not fully established yet, and may
fail, and setting SI_ST_RDY would mean we would not be able to retry to
connect.
This should be backported to 1.9 and 2.0.
This commit depends on 55234e33708c5a584fb9efea81d71ac47235d518.