Console flooded with messages when UDP connection fails

[giuliomoro]

See https://forum.bela.io/d/482-netsend-u-errors/4

This was because the return value from the failed recv() or send() did not cause the [netsend] or [netreceive] object to disconnect and stop trying to use the port. This was a side effect of the threaded implementation, where the error message during the cal was not returned to the object that requested it.

Tentative fix in 3f34416

This involves two extra ring_buffers where failing file descriptors are stored from the io thread, so that the fds can be removed (recv) or the corresponding object _disconnected (send) from the audio thread.

Testing binary:

libpd-xenomai-3-dev_0.10.1-xenomai-dirty-1_armhf.deb.zip

Install instructions:

unzip libpd-xenomai-3-dev_0.10.1-xenomai-dirty-1_armhf.deb.zip
dpkg -i libpd-xenomai-3-dev_0.10.1-xenomai-dirty-1_armhf.deb