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.

/*
 * The structure defined in this header file is returned by the
 * collect_rtpmgr_resp() function, which is a wrapper around
 * the mess of recvmsg with file descriptor passing.
 */

struct rtp_alloc_resp_wrap {
	struct rtp_alloc_resp resp;
	unsigned	resp_len;
	int		fd_buf[4];
	unsigned	num_fd;
};