Make jni_headers more widely available

It's another part of aosp/1276318 to make the jni_headers visible
for modules(e.g. Connectivity module) to fix the code sync issue
between mainline-prod and aosp-master.

Bug: 152482542
Bug: 174281883
Test: m
Change-Id: Ica0fdd9984987359be4087d7b33a226b54a90193
Merged-In: Ifc29bd154022c7f9a4527226e856be72e58e5dfc