hal_tetheroffload: move hwservice mapping to core policy

Addresses:
avc: denied { find } for
interface=android.hardware.tetheroffload.config::IOffloadConfig
scontext=u:r:system_server:s0
tcontext=u:object_r:default_android_hwservice:s0
tclass=hwservice_manager

Bug: 77855688
Test: build/boot Sailfish, turn on tethering, no selinux denial
Change-Id: I97cae0928b5311a4da41d19cbd5c863c3137a49f
(cherry picked from commit 3a346ea7)