Add TEST_MAPPING for network policy related logic.

TEST_MAPPING is included to run network policy related CTS
and unit tests in presubmit whenever network policy related
code changes.

Bug: 142080863
Bug: 137859686
Test: manual
Test: atest --test-mapping services/core/java/com/android/server/net/
Change-Id: I894b21716cd301416890a3a65751808c50e17842