deinterleave: Use GstIterator for iterating all pads instead of manually iterating them while holding the object lock all the time
deinterleave: Use GstIterator for iterating all pads instead of manually iterating them while holding the object lock all the time

Doing queries while holding the object lock is a bit dangerous, and in this
case causes deadlocks.

https://bugzilla.gnome.org/show_bug.cgi?id=763326

Kurento/gst-plugins-good,StreamUtils/gst-plugins-good,GStreamer/gst-plugins-good,hizukiayaka/gst-plugins-good,StreamUtils/gst-plugins-good,stfl/gst-plugins-good,pexip/gst-plugins-good,stfl/gst-plugins-good,GrokImageCompression/gst-plugins-good,Kurento/gst-plugins-good,GrokImageCompression/gst-plugins-good,Kurento/gst-plugins-good,GStreamer/gst-plugins-good,hizukiayaka/gst-plugins-good,pexip/gst-plugins-good,pexip/gst-plugins-good,hizukiayaka/gst-plugins-good,StreamUtils/gst-plugins-good,Kurento/gst-plugins-good,stfl/gst-plugins-good,Kurento/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good,stfl/gst-plugins-good,GrokImageCompression/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good,GrokImageCompression/gst-plugins-good,StreamUtils/gst-plugins-good,hizukiayaka/gst-plugins-good