[IT4.2] Update argument type of interfaceClassDataActivityChanged

The argument type of interfaceClassDataActivityChanged takes a
string for the network type. It requires both the receivers and
NMS to do type transformation. The transformation is a redundant
work. Update it to take integer directly and rename to
understandable naming.

Bug: 170598012
Test: atest FrameworksNetTests
Change-Id: Ibe9fa7a1b71af2dab916b5d615742e77e4174c39