Use a comma instead of a null byte for separating IPs and ports

This was making the client difficult to write as it's not possible
to use any of the string functions to copy the full payload across.

firewall-server/form_message.py

@@ -7,7 +7,7 @@ op = sys.argv[1]
 rest = sys.argv[2:]
 
 if op == "C":
-	payload = "\0".join(rest)
+	payload = ",".join(rest)
 else:
 	payload = " ".join(rest)
 

firewall-server/server_includes/handlers.c

@@ -66,7 +66,7 @@ int handle_check_rule(char *data, size_t len) {
     char* endptr = parse_ip(data, &ip);
     if (endptr == NULL) {
         return HANDLER_ILLEGALARG;
-    } else if (endptr[-1] != '\0') {
+    } else if (endptr[-1] != ',') {
         return HANDLER_ILLEGALARG;
     }