[cleanup] Use const in smux interface

smux_trap and oid_copy should allow read-only source.
diff --git a/lib/smux.h b/lib/smux.h
index bab3587..f5754ed 100644
--- a/lib/smux.h
+++ b/lib/smux.h
@@ -150,11 +150,12 @@
                               size_t, int, oid [], size_t);
 extern int smux_header_generic (struct variable *, oid [], size_t *, 
                                 int, size_t *, WriteMethod **);
-extern int smux_trap (oid *, size_t, oid *, size_t, struct trap_object *, 
+extern int smux_trap (const oid *, size_t, const oid *, size_t, 
+		      const struct trap_object *, 
                       size_t, unsigned int, u_char);
 extern int oid_compare (oid *, int, oid *, int);
 extern void oid2in_addr (oid [], int, struct in_addr *);
-extern void *oid_copy (void *, void *, size_t);
+extern void *oid_copy (void *, const void *, size_t);
 extern void oid_copy_addr (oid [], struct in_addr *, int);
 
 #endif /* _ZEBRA_SNMP_H */