Add synchronized to UidRange getter and dump methods

- The UidRange getter and dump methods which is to access
  mVpnInterfaceUidRanges and mVpnLockdownUidRanges need to guard
  with synchronized to ensure the value won't be changed during
  accessing.
- Also make getVpnLockdownUidRanges() to be a package-private
  method. It's accessed from PermissionMonitorTest only.

Bug: 232048835
Test: FrameworksNetTests CtsNetTestCases
Change-Id: I850f155a01c309f9d75f5143dc0a46a1505415bd
1 file changed