mgw: accept zero-length RTP payload as BFI Mainline OsmoBTS now has an option (rtp continuous-streaming) that causes it to emit an RTP packet every 20 ms without gaps, sending a BFI marker in the form of zero-length RTP payload when it has nothing else to send. These codec-independent BFI markers don't indicate TAF, but this provision is a good start. Accept this BFI packet format in themwi-mgw.

/*
 * This header file holds some definitions for RTP, as this protocol
 * functions in our GSM and PSTN environment.
 */

#define	RTP_PACKET_HDR_SIZE	12
#define	RTP_PACKET_SIZE_PSTN	172
#define	RTP_MAX_PAYLOAD		160

struct rtp_packet {
	uint8_t		v_p_x_cc;
	uint8_t		m_pt;
	uint16_t	seq;
	uint32_t	tstamp;
	uint32_t	ssrc;
	uint8_t		payload[RTP_MAX_PAYLOAD];
};