[NS05] Feed network offer callbacks

The design is very simply expressed :
An offer is needed for a request if and only if that offer
might beat the satisfier for that request.

The implementation of "might beat" is NetworkRanker#mightBeat.

Test: FrameworksNetTests FrameworksWifiTests NetworkStackTests
Bug: 167544279
Merged-In: I3c2563d4ae4e3715d0c6270344ba8f7ef067872f
Merged-In: I0fe911eef2483ecbac48c733d56283b81538690a
Change-Id: I0fe911eef2483ecbac48c733d56283b81538690a
  (cherry-picked from 7b6a33bd504e88ac051db9511eafe915d80e7539)
11 files changed