spice-channel: move out non blocking logic of _flush_wire()
spice-channel: move out non blocking logic of _flush_wire()

This patch introduces spice_channel_flush_wire_nonblocking() helper
without changing any logic.

Related: https://bugs.freedesktop.org/show_bug.cgi?id=96598
Signed-off-by: Victor Toso <39b7599ff73bbf5db531748ba5250f21fa7120ff@redhat.com>
Acked-by: Christophe Fergeau <05b95054a663c388a4e33d95828cb30f0370f8ef@redhat.com>

fgouget/spice-gtk,fgouget/spice-gtk,flexVDI/spice-gtk,fgouget/spice-gtk,flexVDI/spice-gtk