Expose __res_randomid.

I don't think this will help the original submitter, because <resolv.h>
is mostly useless on Android. One day we might have a deprecation and
removal policy for the NDK, but until then we should probably maintain
this header.

Bug: https://github.com/android-ndk/ndk/issues/739
Test: ran tests
Change-Id: I2db859abfdebc3824c997462fa6133d5b355a8dd
diff --git a/tests/resolv_test.cpp b/tests/resolv_test.cpp
index f1d82e4..5743239 100644
--- a/tests/resolv_test.cpp
+++ b/tests/resolv_test.cpp
@@ -58,3 +58,21 @@
   ASSERT_EQ(static_cast<int>(strlen("hello")), b64_pton("aGVsbG8=", buf, sizeof(buf)));
   ASSERT_STREQ(reinterpret_cast<char*>(buf), "hello");
 }
+
+TEST(resolv, p_class) {
+  ASSERT_STREQ("IN", p_class(ns_c_in));
+  ASSERT_STREQ("BADCLASS", p_class(-1));
+}
+
+TEST(resolv, p_type) {
+  ASSERT_STREQ("AAAA", p_type(ns_t_aaaa));
+  ASSERT_STREQ("BADTYPE", p_type(-1));
+}
+
+TEST(resolv, res_init) {
+  ASSERT_EQ(0, res_init());
+}
+
+TEST(resolv, res_randomid) {
+  res_randomid();
+}