Move NetworkUtils JNI out of core/jni

Keep the utilities included via a library, but move them out of
core/jni, and prepare a library to package them together with
framework-connectivity.

Also remove unnecessary dependencies in framework-connectivity.

Bug: 171540887
Test: device boots and has connectivity

Change-Id: I0b55dfe92f3cb6e848d79ac7953756f39aaa2597