Convert IControlsTethering from interface into callback

Additionally:
    - add updateLinkProperties() method to new callback
    - skeletally connect LinkProperties updates through
      to OffloadController

TODOs liberally sprinkled through out.

Test: as follows
    - built
    - flashed
    - booted
    - runtest frameworks-net passes
Bug: 29337859
Bug: 32163131
Change-Id: I631d17b26be153534551a1615931fc98b598b953