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 defines the library interface for "simple"
 * RTP endpoint allocation.
 */

struct rtp_alloc_simple {
	struct sockaddr_storage gsm_addr;
	int	gsm_rtp_fd;
	int	gsm_rtcp_fd;
	struct sockaddr_storage pstn_addr;
	int	pstn_rtp_fd;
	int	pstn_rtcp_fd;
};