[IT4.4] Host network activity related logic into a new class

Create an inner class to handle the network activity related
logic to isolate the code for code cleanliness. It's helpful for
the follow-up modifications to move network activity logic from
NMS to CS to support Connectivityservice mainline.

Bug: 170598012
Test: atest FrameworksNetTests
Change-Id: I33b3b11f2700cb10eb6e3b58b6dfa52251bece80
1 file changed