build: Extend ip_mreq hack to DragonFlyBSD and SunOS

This extends the ip_mreq hack to DragonFlyBSD and SunOS. This has been
in pkgsrc for some time. I've cleaned up the pkgsrc patch a little and
am submitting it upstream. Credit is due to pkgsrc maintainers.

Tested on SmartOS (illumos).

Fixes: #819
Signed-off-by: Greg Troxel <gdt@ir.bbn.com>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/configure.ac b/configure.ac
index eeb2420..75a48e4 100755
--- a/configure.ac
+++ b/configure.ac
@@ -929,7 +929,7 @@
 AC_MSG_CHECKING([for BSD struct ip_mreq hack])
 AC_TRY_COMPILE([#ifdef HAVE_SYS_PARAM_H
 #include <sys/param.h>
-#endif],[#if (defined(__FreeBSD__) && ((__FreeBSD_version >= 500022 && __FreeBSD_version < 700000) || (__FreeBSD_version < 500000 && __FreeBSD_version >= 440000))) || (defined(__NetBSD__) && defined(__NetBSD_Version__) && __NetBSD_Version__ >= 106010000) || defined(__OpenBSD__) || defined(__APPLE__)
+#endif],[#if (defined(__FreeBSD__) && ((__FreeBSD_version >= 500022 && __FreeBSD_version < 700000) || (__FreeBSD_version < 500000 && __FreeBSD_version >= 440000))) || (defined(__NetBSD__) && defined(__NetBSD_Version__) && __NetBSD_Version__ >= 106010000) || defined(__OpenBSD__) || defined(__APPLE__) || defined(__DragonFly__) || defined(__sun)
   return (0);
 #else
   #error No support for BSD struct ip_mreq hack detected