gn2bp: add jni_headers if --sysroot is set in cflags am: f22e9d07c6

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2276597

Change-Id: If3d7f4e1e27e19d188a08a423563bbf4cd649c52
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>