Fix non-IPv6 build post 57785538c6.

57785538c6 change the test for FreeBSD
from __FreeBSD_version to __FreeBSD__. However this test was performed
before sys/param.h was included, therefore __FreeBSD_version was never
defined. As the test was never true opt_random_ip_id.h was never included.

Submitted by:	bdragon
Reported by:	bdragon
MFC after:	1 week
X-MFC with:	57785538c6

sys/contrib/ipfilter/netinet/ip_fil_freebsd.c

@@ -20,10 +20,6 @@ static const char rcsid[] = "@(#)$Id$";
     !defined(KLD_MODULE) && !defined(IPFILTER_LKM)
 # include "opt_inet6.h"
 #endif
-#if defined(__FreeBSD__) && \
-    !defined(KLD_MODULE) && !defined(IPFILTER_LKM)
-# include "opt_random_ip_id.h"
-#endif
 #include <sys/param.h>
 #include <sys/eventhandler.h>
 #include <sys/conf.h>