Move LocationPermissionChecker to libs/net

LocationPermissionChecker was written to be used by multiple
connectivity modules, so it belongs in the frameworks/libs/net library.

The file is moved as-is with minor modifications in the test to avoid
usage of the privileged ActivityManager.getCurrentUser API.

Bug: 181837977
Test: atest NetworkStaticLibTests
Change-Id: I63bce35ba87c45138b3aaf6244367e982dfec455