Clear calling identity in registerNetworkAgent. am: 4b1cd16a76

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

Change-Id: I0f93630527cfe352f5d8f5c69b5276dadbb8c3e4
tree: 0064a9624d0ea17bc52ee9c9a7a71c43cd2c0fa0
  1. core/
  2. services/
  3. tests/