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.

Exempt-From-Owner-Approval: cherry-pick from AOSP

Bug: 150999716
Test: m
Merged-In: I8fd2a3c9b69454c6018c72f5198898bc90dc4d0d
(cherry picked from commit 937b4bf173)
Change-Id: I8fd2a3c9b69454c6018c72f5198898bc90dc4d0d

libstats/push_compat/Android.bp

@@ -49,6 +49,7 @@ cc_library {
         "libstatssocket_headers",
     ],
     static_libs: ["libgtest_prod"],
+    apex_available: ["com.android.resolv"],
 }
 
 cc_test {

libstats/socket/Android.bp

@@ -85,6 +85,7 @@ cc_library_headers {
     name: "libstatssocket_headers",
     export_include_dirs: ["include"],
     host_supported: true,
+    apex_available: ["com.android.resolv"],
 }
 
 cc_benchmark {