Support for Service-Route header (RFC 3608)

[bennylp]

The Service-Route header is used for routing requests in 3GPP/IMS network. UAC would construct the initial route-set based on the URI listed in Service-Route headers.

This support will be done in PJSUA-LIB level.

[bennylp]

Committed initial, untested code in r1507

[bennylp]

Updated in r1508

[bennylp]

Change default behavior in r1520:

• Service-Route processing is now disabled by default, to maintain backward compatibility since lack of S-R will clear the route set for the account.
• Application can enable S-R processing by setting pjsua_acc_config.enable_service_route, or by specifying --service-route option in pjsua.

See also Difference between proxy and outbound proxy setting in the PJSIP FAQ.

[bennylp]

In r1542:

• Changed Service-Route processing to append S-R to existing route set instead of overwriting them.