ippool_new(): const-ify input arguments

Change-Id: If3e53584e8c9c1f06bba4c183c9fd65fae913904
diff --git a/lib/ippool.h b/lib/ippool.h
index 53154f2..e3c1c92 100644
--- a/lib/ippool.h
+++ b/lib/ippool.h
@@ -69,7 +69,7 @@
 extern unsigned long int ippool_hash(struct in46_addr *addr);
 
 /* Create new address pool */
-extern int ippool_new(struct ippool_t **this, char *dyn, char *stat,
+extern int ippool_new(struct ippool_t **this, const char *dyn, const char *stat,
 		      int allowdyn, int allowstat, int flags);
 
 /* Delete existing address pool */