Implement ICE option tag (RFC 5678)

[bennylp]

RFC 5678 describes new SIP option tag and media features tag to indicate support for ICE. Some servers look for this option tag to determine whether relay assistance is to be applied for the endpoint.

The new SIP media feature tag is a parameter +sip.ice which should appear as Contact header parameter in REGISTER request and OPTIONS response, and optionally in other requests.

SIP option tag ice may be used with Require header to indicate that ICE support is mandatory. Note that this option tag SHOULD NOT be used with Supported header.

This ticket supports all of the above, except that to add ice in Require header of outgoing INVITE requests, application would have to add this Require header manually, by adding the header in the pjsua_msg_data parameter when calling pjsua_call_make_call() function.

[bennylp]

(In [3222]) Fixed #1081: Implement ICE option tag (RFC 5678)