Constify arguments.

--- sys/netinet6/in6.h	(svn+ssh://svn.freebsd.org/base/head)	(revision 261548)
+++ sys/netinet6/in6.h	(working copy)
@@ -637,8 +637,8 @@ struct ip6_hdr;
 int	in6_cksum_pseudo(struct ip6_hdr *, uint32_t, uint8_t, uint16_t);
 int	in6_cksum(struct mbuf *, u_int8_t, u_int32_t, u_int32_t);
 int	in6_localaddr(struct in6_addr *);
-int	in6_localip(struct in6_addr *);
-int	in6_addrscope(struct in6_addr *);
+int	in6_localip(const struct in6_addr *);
+int	in6_addrscope(const struct in6_addr *);
 struct	in6_ifaddr *in6_ifawithifp(struct ifnet *, struct in6_addr *);
 extern void in6_if_up(struct ifnet *);
 struct sockaddr;