Add NDK API for getprocnetwork

The API is the getter couterpart for setprocnetwork.
Use it in NetworkUtils so that the NDK API can be the source of truth
for the process network.

Bug: 171540887
Test: atest CtsNetTestCases
Merged-In: I4c7a302df580cec6315e10d0d49a89cf93597ef0
Change-Id: Ibcb8960af2be87d8dd4cf3692293ff65df2904a7