gst/rtpmanager/: Fix some docs.

Original commit message from CVS:
* gst/rtpmanager/rtpjitterbuffer.c: (rtp_jitter_buffer_insert),
(rtp_jitter_buffer_get_sync):
* gst/rtpmanager/rtpsession.c: (on_sender_timeout),
(session_cleanup):
* gst/rtpmanager/rtpsource.c:
Fix some docs.

gst/rtpmanager/rtpjitterbuffer.c

@@ -377,6 +377,7 @@ rtp_jitter_buffer_insert (RTPJitterBuffer * jbuf, GstBuffer * buf,
   time = calculate_skew (jbuf, rtptime, time, clock_rate);
   GST_BUFFER_TIMESTAMP (buf) = time;
 
+  /* It's more likely that the packet was inserted in the front of the buffer */
   if (G_LIKELY (list))
     g_queue_insert_before (jbuf->packets, list, buf);
   else

gst/rtpmanager/rtpsession.c

@@ -1815,6 +1815,7 @@ ignore:
  * @buffer: an RTP buffer
  * @current_time: the current system time
  * @ntpnstime: the NTP time in nanoseconds of when this buffer was captured.
+ * This is the buffer timestamp converted to NTP time.
  *
  * Send the RTP buffer in the session manager. This function takes ownership of
  * @buffer.

gst/rtpmanager/rtpsource.c

@@ -970,7 +970,8 @@ rtp_source_process_bye (RTPSource * src, const gchar * reason)
  * rtp_source_send_rtp:
  * @src: an #RTPSource
  * @buffer: an RTP buffer
- * @ntpnstime: the NTP time when this buffer was captured in nanoseconds
+ * @ntpnstime: the NTP time when this buffer was captured in nanoseconds. This
+ * is the buffer timestamp converted to NTP time.
  *
  * Send an RTP @buffer originating from @src. This will make @src a sender.
  * This function takes ownership of @buffer and modifies the SSRC in the RTP