* nta: NULL host and port in user Via are filled automaticaly

  NULL host or port in user-supplied Via header will be filled
  automaticaly by NTA, just like branch and rport params.

  Added related test case to test_nta_api.c.



git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@10826 d0543943-73ff-0310-b7d9-9358b9ac24b2