[Tether18] Add file_contexts for com.android.tethering.apex

Bug: 144320626
Test: build

Change-Id: I6b5c079a917524bf4f1ad3f89b1f44708f0d6ed7
diff --git a/apex/com.android.tethering.apex-file_contexts b/apex/com.android.tethering.apex-file_contexts
new file mode 100644
index 0000000..9398505
--- /dev/null
+++ b/apex/com.android.tethering.apex-file_contexts
@@ -0,0 +1 @@
+(/.*)?           u:object_r:system_file:s0