This change store localOnly wifi clients in its own field so that
tethered and localOnly hotspot clients can exist at the same time.

Currently, there are no tethered and localOnly hotspot clients at
the same time because PrivateAddressCoordinator does not support
SAP + LOHS. A follow-up change will be made to allow this.

When both SAP and LOHS are enabled, the SAP and LOHS clients from
TetheringEventCallback#onClientsChanged are all TETHERING_WIFI.
Currently, there is no way for the listeners to distinguish between
SAP and LOHS clients.

Bug: 233175023
Test: atest TetheringTests
(cherry picked from https://android-review.googlesource.com/q/commit:ae3abdfa4be2e4867d4cad70be15f90ad36a0b32)
Merged-In: I01b0a6abb084f7135f7825e0c5303e49c16a4c39
Change-Id: I01b0a6abb084f7135f7825e0c5303e49c16a4c39