Allow SAP and LOHS wifi clients exist at the same time

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
Change-Id: I01b0a6abb084f7135f7825e0c5303e49c16a4c39