Add new network process capability.

- Introduce network capability which allows apps to access network
  despite power restrictions.
- Update NPMS to allow apps network access only if they are in a
  higher proc_state or they are hodling the new network capability.

Bug: 177641226
Test: atest ./services/tests/servicestests/src/com/android/server/net/NetworkPolicyManagerServiceTest.java
Test: atest ./tests/cts/hostside/src/com/android/cts/net/HostsideRestrictBackgroundNetworkTests.java
Change-Id: Ia411ddef2e8cb77d371c22262d5b1e06a0396e29