Move offload config hidl usage from native to java

TetheringUtil JNI is too big that it statically linking hidl and its
dependency library. To remove these static libraries, calling hidl in java
directly instead of using JNI.

Bug: 148984662
Test: -build, flash, boot
      -manually ON/OFF tethering

Change-Id: Id5a9759eb453fddaf0c3b7a31da17224e35e963e