Allow EJs to obtain new network capability.

- Introduce new oom_adj score to be used for EJs so that they won't
  be killed before normal jobs but before any FGS. Also, add a new
  bind flag to instruct the OomAdjuster about when to use this
  new oom_adj score.
- Unlike other capabilities, any app (regardless of it's proc_state)
  with network capability will be able to transfer it's capability
  to other app by binding to it.

Bug: 177641226
Test: atest ./tests/app/src/android/app/cts/ActivityManagerProcessStateTest.java
Test: atest ./tests/cts/hostside/src/com/android/cts/net/HostsideRestrictBackgroundNetworkTests.java
Test: atest ./services/tests/mockingservicestests/src/com/android/server/am/MockingOomAdjusterTests.java
Test: atest CtsJobSchedulerTestCases

Change-Id: I888764ff22fba92fe2cccf3d8442ed318a19ad2a