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

libc/upstream-openbsd/lib/libc/net/inet_netof.c

@@ -0,0 +1,50 @@
+/*	$OpenBSD: inet_netof.c,v 1.6 2005/08/06 20:30:03 espie Exp $ */
+/*
+ * Copyright (c) 1983, 1993
+ *	The Regents of the University of California.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/param.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+/*
+ * Return the network number from an internet
+ * address; handles class a/b/c network #'s.
+ */
+in_addr_t
+inet_netof(struct in_addr in)
+{
+	in_addr_t i = ntohl(in.s_addr);
+
+	if (IN_CLASSA(i))
+		return (((i)&IN_CLASSA_NET) >> IN_CLASSA_NSHIFT);
+	else if (IN_CLASSB(i))
+		return (((i)&IN_CLASSB_NET) >> IN_CLASSB_NSHIFT);
+	else
+		return (((i)&IN_CLASSC_NET) >> IN_CLASSC_NSHIFT);
+}