flattened apex: fix clatd mode also for inprocess tethering

This is a follow-on CL for aosp/2528043

/system/apex/com.android.tethering.inprocess/bin/for-system/clatd
is bind mounted as /apex/com.android.tethering/bin/for-system/clatd
when using inprocess tethering.

Bug: 273821347
Test: `ls -l /apex/com.android.tethering/bin/for-system/clatd` on bertha
Test: Also see aosp/2528043 for how it is tested
Change-Id: Ia20165663e4ff6d9266fe601d25395816792a3f7