v4l2bufferpool: Update allocator flags
v4l2bufferpool: Update allocator flags

When we hit emulated formats, we disable CREATE_BUFS since libv4l2
cope very badly with it. Also clear the allocator flags so we will
never try to allocate more buffers. This fixes failure when the copy
threshold is reached as we where calling CREATE_BUFS, which lead to
libv4l2 instability.

pexip/gst-plugins-good,StreamUtils/gst-plugins-good,rawoul/gst-plugins-good,sh0/gst-plugins-good,veo-labs/gst-plugins-good,kittee/gst-plugins-good,chamois94/gst-plugins-good,stfl/gst-plugins-good,shelsonjava/gst-plugins-good,ikonst/gst-plugins-good,veo-labs/gst-plugins-good,stfl/gst-plugins-good,froggatt/gst-plugins-good-m,StreamUtils/gst-plugins-good,Kurento/gst-plugins-good,ijsf/OpenWebRTC-gst-plugins-good,Kurento/gst-plugins-good,freedesktop-unofficial-mirror/gstreamer__gst-plugins-good,sebras/gst-plugins-good,chamois94/gst-plugins-good,pexip/gst-plugins-good,froggatt/gst-plugins-good-m,hizukiayaka/gst-plugins-good,chamois94/gst-plugins-good,GrokImageCompression/gst-plugins-good,loshca/gst-plugins-good,sebras/gst-plugins-good,sh0/gst-plugins-good,pexip/gst-plugins-good,froggatt/gst-plugins-good-m,kittee/gst-plugins-good,GStreamer/gst-plugins-good,ikonst/gst-plugins-good,kittee/gst-plugins-good,vatavuserban/gst-plugins-good,BigBrother-International/gst-plugins-good,hizukiayaka/gst-plugins-good,Kurento/gst-plugins-good,sh0/gst-plugins-good,freedesktop-unofficial-mirror/gstreamer__gst-plugins-good,stfl/gst-plugins-good,stfl/gst-plugins-good,freedesktop-unofficial-mirror/gstreamer__gst-plugins-good,vatavuserban/gst-plugins-good,vatavuserban/gst-plugins-good,loshca/gst-plugins-good,rawoul/gst-plugins-good,GStreamer/gst-plugins-good,loshca/gst-plugins-good,sebras/gst-plugins-good,ijsf/OpenWebRTC-gst-plugins-good,GStreamer/gst-plugins-good,rawoul/gst-plugins-good,Kurento/gst-plugins-good,ikonst/gst-plugins-good,shelsonjava/gst-plugins-good,GStreamer/gst-plugins-good,froggatt/gst-plugins-good-m,StreamUtils/gst-plugins-good,rawoul/gst-plugins-good,ikonst/gst-plugins-good,loshca/gst-plugins-good,GrokImageCompression/gst-plugins-good,ijsf/OpenWebRTC-gst-plugins-good,chamois94/gst-plugins-good,Kurento/gst-plugins-good,veo-labs/gst-plugins-good,GrokImageCompression/gst-plugins-good,BigBrother-International/gst-plugins-good,vatavuserban/gst-plugins-good,StreamUtils/gst-plugins-good,shelsonjava/gst-plugins-good,sebras/gst-plugins-good,veo-labs/gst-plugins-good,pexip/gst-plugins-good,freedesktop-unofficial-mirror/gstreamer__gst-plugins-good,pexip/gst-plugins-good,hizukiayaka/gst-plugins-good,hizukiayaka/gst-plugins-good,BigBrother-International/gst-plugins-good,ijsf/OpenWebRTC-gst-plugins-good,kittee/gst-plugins-good,GrokImageCompression/gst-plugins-good,BigBrother-International/gst-plugins-good,sh0/gst-plugins-good,shelsonjava/gst-plugins-good