Make ipsec file_contexts as "android:path" property

It follows examples of other APEX to make file_contexts of ipsec
module as "android:path" property

Bug: 143192273
Test: atest ipsec_e2e_tests
Change-Id: Idbba1f964aad7e54077ac77250f9cfd6a6b5049e
diff --git a/apex/Android.bp b/apex/Android.bp
index 8eedfab..13bc49a 100644
--- a/apex/Android.bp
+++ b/apex/Android.bp
@@ -63,6 +63,13 @@
 }
 
 filegroup {
+  name: "com.android.ipsec-file_contexts",
+  srcs: [
+    "com.android.ipsec-file_contexts",
+  ],
+}
+
+filegroup {
   name: "com.android.i18n-file_contexts",
   srcs: [
     "com.android.i18n-file_contexts",