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 the structure used to capture the result
 * of From header field parsing.
 */

struct grok_from {
	char		*uri;
	unsigned	uri_len;
	char		*user;
	unsigned	user_len;
	char		*cnam;
	unsigned	cnam_len;
	int		cnam_quoted;
};