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
Merged-In: I178130e65db4fef26d62ea7eaa9a52f7e8103432
Merged-In: I832d77747de7517513c22d36fff4a2fa2bb95154
Change-Id: I631d17b26be153534551a1615931fc98b598b953
(cherry picked from commit ab6439b0)