Add apex_available to libnetutils

The library is included by the tethering module, and was allowlisted
for compatibility purposes, but needs to have the rule applied.

Bug: 171540887
Test: m
Change-Id: Ic02c559d6e82fb41c33ba723bd06ef708e7baaa9

libnetutils/Android.bp

@@ -21,6 +21,11 @@ cc_library_shared {
     cflags: ["-Werror"],
 
     export_include_dirs: ["include"],
+    // TODO: remove connectivity module dependency, or have this lib build against the ndk
+    apex_available: [
+        "//apex_available:platform",
+        "com.android.tethering",
+    ],
 }
 
 cc_library_static {