Clear calling identity in registerNetworkAgent. am: 4b1cd16a76 am: 964f7c7e4d

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1511317

Change-Id: Ia731c724f32a52d609db513f07ac4615343ee0ad
tree: 0064a9624d0ea17bc52ee9c9a7a71c43cd2c0fa0
  1. core/
  2. services/
  3. tests/