Use the latest stable netd AIDL interface in Tethering.

This is required to use the new BPF tethering APIs that set data
usage limits.

AOSP and master are already using -unstable instead of -V3.
In order not to change master, the Merged-In tag is set to the CL
that switched AOSP (and master) to -unstable.

Test: m
Bug: 150736748
Merged-In: I2d2cedf560319653f67f6b06f7abb0bf66eba91a
Change-Id: Idba29b0fe428ac6552a025dcbe15729739088e9e