Allow vendor code to link to libandroid_net.

This library contains only the multinetwork API, which is part
of the NDK and has long-term support. It is needed by any native
that wants to use network communications on a different network
than the default network, and thus is necessary for vendor code
such as IMS clients or carrier applications.

Bug: 37527489
Test: marlin builds and boots
Test: MultinetworkApiTest CTS tests passes
Change-Id: I2aa592d1d082aae410173adf2a09f6d1dd8092dc
diff --git a/native/android/Android.bp b/native/android/Android.bp
index 452adc0..00fe638 100644
--- a/native/android/Android.bp
+++ b/native/android/Android.bp
@@ -87,3 +87,10 @@
 
     include_dirs: ["bionic/libc/dns/include"],
 }
+
+llndk_library {
+    name: "libandroid_net",
+    export_include_dirs: ["include"],
+    symbol_file: "libandroid_net.map.txt",
+    unversioned: true,
+}