Flesh out <arpa/inet.h>.

Use the upstream OpenBSD implementations of these functions.

Also ensure we have symbols for htonl, htons, ntohl, and ntohs.
gtest doesn't like us using the macro versions in ASSERT_EQ.

Bug: 14840760
Change-Id: I68720e9aca14838df457d2bb27b999d5818ac2b5
diff --git a/tests/Android.mk b/tests/Android.mk
index b17492a..4ad07ba 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -44,6 +44,7 @@
     -std=gnu++11 \
 
 libBionicStandardTests_src_files := \
+    arpa_inet_test.cpp \
     buffer_tests.cpp \
     ctype_test.cpp \
     dirent_test.cpp \