PermissionMonitor: Move intent receiver to ConnectivityService.

Currently, PermissionMonitor listen to user add/remove and
package add/remove intent respectively, and so does VPN.
Thus, races might occurr between them.

This commit refactor PermissionMonitor part by using
ConnectivityService to listen to intents and dispatch events
to PermissionMonitor.

Bug: 118811303
Test: 1. atest FrameworksNetTests
      2. manually add/remove package

Change-Id: I6e45b5870d5b1300cad252d25bdb4da78f9bf70e