defrag: fix timeout setting when config is missing

When the config is missing, DefragPolicyGetHostTimeout will default
to returning -1. This will effectively set no timeout at all, leading
to defrag trackers being freed too early.

src/defrag-config.c

@@ -96,7 +96,8 @@ int DefragPolicyGetHostTimeout(Packet *p)
         timeout = DefragPolicyGetIPv4HostTimeout((uint8_t *)GET_IPV4_DST_ADDR_PTR(p));
     else if (PKT_IS_IPV6(p))
         timeout = DefragPolicyGetIPv6HostTimeout((uint8_t *)GET_IPV6_DST_ADDR(p));
-    else
+
+    if (timeout <= 0)
         timeout = default_timeout;
 
     return timeout;