build: remove AIX, NEC EWS and IRIX

Valar morghulis.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
Acked-by: Greg Troxel <gdt@ir.bbn.com>
Acked-by: Feng Lu <lu.feng@6wind.com>
Acked-by: Paul Jakma <paul@jakma.org>
diff --git a/zebra/ipforward_sysctl.c b/zebra/ipforward_sysctl.c
index 185aee3..8824418 100644
--- a/zebra/ipforward_sysctl.c
+++ b/zebra/ipforward_sysctl.c
@@ -106,7 +106,7 @@
 {
   CTL_NET,
   PF_INET6,
-#if defined(KAME) || (defined(__bsdi__) && _BSDI_VERSION >= 199802 ) || defined(NRL)
+#if defined(KAME) || defined(NRL)
   IPPROTO_IPV6,
   IPV6CTL_FORWARDING
 #else /* NOT KAME */