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.

/*
 * Here we define struct sip_resp_ident, a structure that captures
 * Call-ID and CSeq headers from initial parsing of SIP responses,
 * allowing these responses to be matched with call state and
 * with UAC requests that elicited them.
 */

struct sip_resp_ident {
	char		*call_id;
	unsigned	cseq_num;
	char		*cseq_method;
	char		*error_field;
};