Add utilities to test tap interface networks

Add an ArpResponder based on a generic PacketResponder class, and a
TestHttpServer based on NanoHttpd.

Test: tests based on these utilities
Bug: 160617623
Bug: 160656765
Change-Id: I50b872a8b23e8df997e8f62f0adc7c0256c4d74d
diff --git a/staticlibs/Android.bp b/staticlibs/Android.bp
index 4b15b16..f4799f0 100644
--- a/staticlibs/Android.bp
+++ b/staticlibs/Android.bp
@@ -98,6 +98,7 @@
     ],
     static_libs: [
         "androidx.test.ext.junit",
+        "libnanohttpd",
         "net-tests-utils-host-device-common",
         "net-utils-device-common",
     ],