firewall3: fix typo that affects ICMPv6 rules with numeric icmp_type

Problem can be reproduced with a rule like this:
   option src 'wan'
   option family 'ipv6'
   option proto 'icmp'
   option icmp_type '128'
   option target 'DROP'
The resulted rule will set --icmpv6-type to 128/255.

Signed-off-by: Alin Nastac <alin.nastac@gmail.com>

options.c

@@ -568,7 +568,7 @@ fw3_parse_icmptype(void *ptr, const char *val, bool is_list)
 		}
 
 		icmp.type6     = icmp.type;
-		icmp.code6_min = icmp.code_max;
+		icmp.code6_min = icmp.code_min;
 		icmp.code6_max = icmp.code_max;
 
 		v4 = true;