Don't compiled ip6_randomid() in if RANDOM_IP_ID is not defined.

sys/netinet6/ip6_id.c

@@ -98,6 +98,8 @@
 #include <netinet/ip6.h>
 #include <netinet6/ip6_var.h>
 
+#ifdef RANDOM_IP_ID
+
 #ifndef INT32_MAX
 #define INT32_MAX	0x7fffffffU
 #endif
@@ -245,3 +247,5 @@ ip6_randomid(void)
 
 	return randomid(&randomtab_32);
 }
+
+#endif /* RANDOM_IP_ID */

sys/netinet6/ip6_var.h

@@ -353,7 +353,9 @@ int	rip6_usrreq __P((struct socket *,
 int	dest6_input __P((struct mbuf **, int *, int));
 int	none_input __P((struct mbuf **, int *, int));
 
+#ifdef RANDOM_IP_ID
 u_int32_t ip6_randomid __P((void));
+#endif
 #endif /* _KERNEL */
 
 #endif /* !_NETINET6_IP6_VAR_H_ */