filter: fix pfb_arb_resampler XML for I/O types
udp: fix udp_source to avoid permanent work blockage
blocks: added proper EOF for msg tags test
digital: context yield for header_payload_demux
blocks: pdu_to_tagged_stream_impl fix get message

Switched call from blocking to nowait.

* The code now matches up with the intention/comments
* Its bad form to block the work function indefinitely
* The QA tests continue to pass
Merge branch 'maint'