Changes

ttcn3-asterisk: extensions.conf: Reject subsequent MO/MT calls in VoLTE when busy

Reject calls when the VoLTE endpoint is already busy with an ongoing
call.

Related: SYS#7003
Change-Id: If4ce1fee36e51ac72681ac2ce04531d501ccb56c

ttcn3-asterisk: extensions.conf: Reject calls if all SIP UAs busy in call

Before this patch, asterisk would ring on local SIP UAs already in a
call, which is not the expected behavior for this project.

Related: SYS#7003
Change-Id: Id9e3ead6e28a53793c6cceb6f23d5e6d987521d8