Add TetherConfigParcel to improve startTetheringWithConfiguration

In order to support extensibility, update the interface between
netd to take a configuration parcel, instead of fixed
parameters.

Bug: 145777247
Test: atest FrameworksNetTests
Test: build, flash, on/off tethering
Change-Id: I3dbccc46ce4ddccfb6d518de240e4604b7f95eed