am df08c2f0: am 692cac9f: SipHelper: add debug log for challenge responses.

Merge commit 'df08c2f03e7cf7be7002d34efe8e4e8d24e406de'

* commit 'df08c2f03e7cf7be7002d34efe8e4e8d24e406de':
  SipHelper: add debug log for challenge responses.