lib: make masklen2ip() safer and faster
diff --git a/lib/prefix.h b/lib/prefix.h
index 1cb91b2..4233464 100644
--- a/lib/prefix.h
+++ b/lib/prefix.h
@@ -176,7 +176,7 @@
extern void apply_classful_mask_ipv4 (struct prefix_ipv4 *);
extern u_char ip_masklen (struct in_addr);
-extern void masklen2ip (int, struct in_addr *);
+extern void masklen2ip (const int, struct in_addr *);
/* returns the network portion of the host address */
extern in_addr_t ipv4_network_addr (in_addr_t hostaddr, int masklen);
/* given the address of a host on a network and the network mask length,