* ipaddr.h: add IPADDR_MAX define

src/ipaddr.h

@@ -5,10 +5,12 @@
 
 #include "matches.h"
 
+#define IPADDR_MAX 48 /* 8 x "ffff" + 7 x "::" + '\0' */
+
 typedef struct f2b_ipaddr_t {
   struct f2b_ipaddr_t *next;
   int type;
-  char text[40]; /* 8 x "ffff" + 7 x ":" + '\0' */
+  char text[IPADDR_MAX];
   bool banned;
   union {
     struct in_addr  v4;