Set apex_available property

The marked library(ies) were available to the APEXes via the
hand-written whitelist in build/soong/apex/apex.go. Trying to remove the
whitelist by adding apex_available property to the Android.bp of the
libraries.

Bug: 150999716
Test: m
Change-Id: I8fd2a3c9b69454c6018c72f5198898bc90dc4d0d
diff --git a/libstats/socket/Android.bp b/libstats/socket/Android.bp
index 9fd9fbc..690dc94 100644
--- a/libstats/socket/Android.bp
+++ b/libstats/socket/Android.bp
@@ -54,6 +54,7 @@
     name: "libstatssocket_headers",
     export_include_dirs: ["include"],
     host_supported: true,
+    apex_available: ["com.android.resolv"],
 }
 
 cc_benchmark {