audio: Reset rate control when adding bytes

Commit 90320051ea ("spiceaudio: add a pcm_ops buffer_get_free
function") caused to emit messages saying "Resetting rate control"
frequently when the guest generates no frames.

audio_rate_peek_bytes() resets the rate control when frames < 0 ||
frames > 65536 where frames is the rate-limited number of frames.
Resetting when frames < 0 is sensible as the number simply doesn't make
sense.

There is a problem when frames > 65536. It implies the guest stopped
generating frames for a while so it makes sense to reset the rate
control when the guest resumed generating frames. However, the
commit mentioned earlier broke this assumption by letting spiceaudio
call audio_rate_peek_bytes() whether the guest is generating frames or
not.

Reset the rate control in audio_rate_add_bytes(), which is called only
when actually adding frames, according to the previous call to
audio_rate_peek_bytes() to avoid frequent rate control resets even when
the guest generates no frame.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Message-Id: <20250317-rate-v1-1-da9df062747c@daynix.com>

audio/audio_int.h

@@ -255,6 +255,7 @@ const char *audio_application_name(void);
 typedef struct RateCtl {
     int64_t start_ticks;
     int64_t bytes_sent;
+    int64_t peeked_frames;
 } RateCtl;
 
 void audio_rate_start(RateCtl *rate);