spice_timer_queue: don't call timers repeatedly
spice_timer_queue: don't call timers repeatedly

For channels that don't run as part of the main loop, we use
spice_timer_queue, while for the other channels we use
qemu timers support. The callbacks for setting timers are supplied to
red_channel via SpiceCoreInterface, and their behavior should be
consistent. qemu timers are called only once per each call to
timer_start. This patch assigns the same behaviour to spice_timer_queue.

freedesktop-unofficial-mirror/spice__spice,elmarco/spice,Fantu/spice,elmarco/spice,freedesktop-unofficial-mirror/spice__spice,Fantu/spice,SPICE/spice,Fantu/spice,freedesktop-unofficial-mirror/spice__spice,elmarco/spice,alon/spice-server,ya-mouse/spice,alon/spice-server,ya-mouse/spice,fgouget/spice,freedesktop-unofficial-mirror/spice__spice,alon/spice-server,SPICE/spice,fgouget/spice,SPICE/spice,freedesktop-unofficial-mirror/spice__spice,elmarco/spice,Fantu/spice,elmarco/spice,alon/spice-server,fgouget/spice,alon/spice-server,fgouget/spice,ya-mouse/spice