Make interface IP serving code set LinkProperties

Additionally, clean up awkward IPv6TetheringInterfaceServices
instantiation mechanics.  In future, this class will be absorbed
by TetherInterfaceStateMachine (prior to its renaming to IpServer).

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

Merged-In: I8b15edbf04c10cd9429da079c6b79352a6740b3b
Merged-In: I39a1744a7fa9b91e3b607429c79f39578e9bde19
Merged-In: I753ab701f2109c0972816724e73119dc1dbc4dca
Change-Id: Ib620e3df182f9f8e2c019aae1cd8981eb0b29376
(cherry picked from commit dd4d5820)