channel: reset channel state to unconnected
channel: reset channel state to unconnected

After coroutine has exited, reset channel state to unconnected,
this allows recycling a channel for reconnection, even in "normal"
disconnect/reconnect cases.

flexVDI/spice-gtk,fgouget/spice-gtk,Fantu/spice-gtk,guodong/spice-gtk,elmarco/spice-gtk,SPICE/spice-gtk,elmarco/spice-gtk,Fantu/spice-gtk,fgouget/spice-gtk,elmarco/spice-gtk,SPICE/spice-gtk,SPICE/spice-gtk,guodong/spice-gtk,Fantu/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,Fantu/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,SPICE/spice-gtk,fgouget/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,elmarco/spice-gtk,guodong/spice-gtk,flexVDI/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,guodong/spice-gtk