Add missing library of services.net

Tethering.java creates an anonymous implementation of IpServer.Callback.
robotests has static link to services.core. services.core and services.net
are merged into services in services/Android.bp.

Therefore, module FrameworksServicesLib should include both services.core
and services.net as static library.

Bug: 119401516
Test: m -j MODULES-IN-frameworks-base-services-robotests
 m -j MODULES-IN-frameworks-base

Change-Id: I4bca54e01528b87375cbcc4d9caf9e5789734b9a