Do not use DMA-BUFs for screensharing when the other side doesn't support it

Recent WebRTC has implemented proper screensharing support with DMA-BUFs and it has been already released with Chrome 96. Problem is that there are cases when DMA-BUFS is not supposed to be used, as of now it should be used only when PipeWire is new enough and both sides advertise DMA-BUFs modifiers. WebRTC doesn't advertise SPA_DATA_DmaBuf buffer type in this case and fallbacks to SPA_DATA_MemFd, however, Mutter (3.32 + related backports) in RHEL 8.5 seems to ignore that and sends SPA_DATA_DmaBuf buffers to us, which we fail to process. This results into broken screensharing.