Jarjar frameworks/libs/net in NetworkStack module

Classes in com.android.net.module.util need to be jarjared to the
module's own package. These classes are imported by several modules and
the framework from frameworks/libs/net.

Test: m
Bug: 149403767
(clean cherry-pick from internal branch)
Merged-In: Id49fdf17fcf48a21455b7fe768ba046b81c51303
Change-Id: Id49fdf17fcf48a21455b7fe768ba046b81c51303