am b57f236e: Merge changes Icf7d67e2,Ia914ec88,I2490ad75,Ie79f2d28 into mnc-dev

* commit 'b57f236e30d87bdfa69bb99e6b3f5ec6a3cc07c7':
  Add a hidden method to clear NetworkCapabilities.
  Fix javadoc error for requestNetwork.
  Simplify network callback handling code.
  Document and unhide CALLBACK_PRECHECK.