[CS] Add an option to block sensitive network specifier

Network specifiers are used for 2 purposes:

- As part of network requests to specify more information on the type
  of requested networks.
- On network agents to specify information about their networks.

The network specifiers of the requests and agents are matched to each
other. However, the agent network specifier may contain sensitive
information which we do not want forwarded to any app.

This CL adds an option to strip out this agent network specifier before
the network capabilities are forwarded to the app.

Bug: 161853197
Bug: 161370134
Test: atest ConnectivityServiceTest (frameworks/base/tests/net)
Test: atest frameworks/base/tests/net
Test: atest frameworks/opt/net/wifi/tests/wifitests
Test: atest frameworks/opt/telephony/tests/telephonytests
Test: atest frameworks/opt/net/ethernet/tests
Test: atest android.net.cts - some flakiness!
Test: act.py ThroughputTest
Test: act.py DataPathTest
Test: atest SingleDeviceTest (cts)
Change-Id: I38ed3ff88532ef522ab167c88d87e6e82295ffc5
Merged-In: If08d312ff814bdde1147518f923199e6349503d5