Update for INVITE getting 504 with XML triggering re-register, REF 14826

* Retrieve information regarding 504-register status while 504 re-register happened.
* Skip playing tone and keep the dialed number and context if 504-register ongoing
  while the original session(INVITE session that got 504 with xml) hangup.
* Call again if 504-register success
* Play congestion tone and reset the info that kept above(context and ext) if
  504-register failed