Migrate libandroid headers to ndk_headers.

Test: make native
Bug: http://b/30465923
Change-Id: I0ef0b3630670241c4efd22515b6ab13eb41a81b3
diff --git a/include/android/multinetwork.h b/include/android/multinetwork.h
index 6c718c9..be01518 100644
--- a/include/android/multinetwork.h
+++ b/include/android/multinetwork.h
@@ -51,6 +51,7 @@
  * on failure with an appropriate errno value set.
  */
 
+#if __ANDROID_API__ >= 24
 
 /**
  * Set the network to be used by the given socket file descriptor.
@@ -104,6 +105,8 @@
         const char *node, const char *service,
         const struct addrinfo *hints, struct addrinfo **res);
 
+#endif /* __ANDROID_API__ >= 24 */
+
 __END_DECLS
 
 #endif  // ANDROID_MULTINETWORK_H