sip-in: default use-100rel to no BulkVS servers act badly when we send a reliable 180 Ringing response to an incoming call, even though they advertise 100rel support in the Supported header in the INVITE packet, and we probably won't be implementing 100rel for outbound because doing per-the-spec PRACK as a UAC is just too burdensome. Therefore, we need to consider 100rel extension as not-really-supported in themwi-system-sw.

/*
 * 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;
};