Add DEFAULT_NETWORK_PRIORITY constants

- Add default network priority to NetworkRequestInfo.
- The default network priority value is used when issue uid
  ranges rules to netd. Netd will use the priority value and uid
  ranges to generate corresponding ip rules specific to the given
  network preference.

Bug: 171872461
Test: atest FrameworksNetTests
Merged-In: I0ea71b348492aeb4784d487bed4cfd5d387426ba

Change-Id: I0ea71b348492aeb4784d487bed4cfd5d387426ba
2 files changed