Add aconfig flag file

This CL does not have Merged-In since all the branches should have the
aconfig file so that adding flags to the file does not have conflicts.
Following CL adds aconfig_declarations to Android.bp only on branches
where aconfig soong targets are supported

Bug: 267870186
Test: TH
Change-Id: I621228a2c9594bf7bfe1cf335619c417e9339743

common/Android.bp

@@ -19,6 +19,10 @@ package {
     default_applicable_licenses: ["Android-Apache-2.0"],
 }
 
+// This is a placeholder comment to avoid merge conflicts
+// as the above target may not exist
+// depending on the branch
+
 java_library {
     name: "connectivity-net-module-utils-bpf",
     srcs: [

common/flags.aconfig

@@ -0,0 +1,8 @@
+package: "com.android.net.flags"
+
+flag {
+  name: "track_multiple_network_activities"
+  namespace: "android_core_networking"
+  description: "NetworkActivityTracker tracks multiple networks including non default networks"
+  bug: "267870186"
+}