ao_pulse: lower default buffer size from 1000ms to 250ms

1000ms is a bit insane. It makes behavior on playback speed changes
worse (because the player has to catch up the dropped audio due to
audio-chain reset), and perhaps makes seeking slower.

Note that the problem of playback speed changes misbehaving will be
fixed in the future, but even then we don't want to have a buffer that
large.

DOCS/man/en/ao.rst

@@ -130,7 +130,7 @@ Available audio output drivers are:
         Set the audio buffer size in milliseconds. A higher value buffers
         more data, and has a lower probability of buffer underruns. A smaller
         value makes the audio stream react faster, e.g. to playback speed
-        changes. Default: 1000.
+        changes. Default: 250.
 
 ``portaudio``
     PortAudio audio output driver. This works on all platforms, and has

audio/out/ao_pulse.c

@@ -621,7 +621,7 @@ const struct ao_driver audio_out_pulse = {
     .resume    = resume,
     .priv_size = sizeof(struct priv),
     .priv_defaults = &(const struct priv) {
-        .cfg_buffer = 1000,
+        .cfg_buffer = 250,
     },
     .options = (const struct m_option[]) {
         OPT_STRING("host", cfg_host, 0),