Temporarily turn background network restrictions off

Adding a constant field to turn off the feature at compile time.
After verification of local builds and tests, when the feature is ready
for staging, the boolean can be flipped to true or removed.

Test: atest CtsHostsideNetworkTests
Test: atest resolv_integration_test
Test: atest FrameworksServicesTests:NetworkPolicyManagerServiceTest

Bug: 304347838
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:21eb0750809b80b154aad628ed6d349ce3f38cbb)
Merged-In: I42c375e8a948f95e79f898cb09bb5c1b859ae113
Change-Id: I42c375e8a948f95e79f898cb09bb5c1b859ae113