fix overriding of previously-received RTP packets that leaded to crashes

RTP packets were previously take from a buffer pool. This was messing
up the Client, since that buffer pool was used by multiple routines at
once, and was probably messing up the Server too, since packets can be
pushed to different queues and there's no guarantee that these queues
have an overall size less than ReadBufferCount.

This buffer pool is removed; this decreases performance but avoids bugs.

client.go

@@ -236,7 +236,6 @@ type Client struct {
 	medias             map[*media.Media]*clientMedia
 	tcpMediasByChannel map[int]*clientMedia
 	lastRange          *headers.Range
-	rtpPacketBuffer    *rtpPacketMultiBuffer // play
 	checkStreamTimer   *time.Timer
 	checkStreamInitial bool
 	tcpLastFrameTime   *int64
@@ -630,7 +629,6 @@ func (c *Client) playRecordStart() {
 
 	if c.state == clientStatePlay {
 		c.keepaliveTimer = time.NewTimer(c.keepalivePeriod)
-		c.rtpPacketBuffer = newRTPPacketMultiBuffer(uint64(c.ReadBufferCount))
 
 		switch *c.effectiveTransport {
 		case TransportUDP: