jack: Fix hanging applications when using jack plugin

jack: Fix hanging applications when using jack plugin

As described in issue #2727

   https://bugtrack.alsa-project.org/alsa-bug/view.php?id=2727

applications hang after some seconds when using the jack plugin.

Kevin Ross <kevin@familyross.net> writes:

   The cause: The plugin creates a pipe, so that the fd's could be
   polled to indicate completion of a transfer.  However, the call to
   write() blocks when playing audio, as nothing actually reads from the
   pipe, and it fills up until it blocks.

   Making the socket non-blocking fixes the problem, and testing with
   playback and capture both work properly for me now.

[Adrian: I've also tested Kevin's patch and confirm it works.]

Signed-off-by: Adrian Knoth <adi@drcomp.erfurt.thur.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>