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
19 files changed