bgpd: Treat numbered community-list only if it's in a range 1-500

bgpd: Treat numbered community-list only if it's in a range 1-500

Before this patch, if we set something like:

```
bgp extcommunity-list expanded 1234 permit admin
```

In running config we have:

```
bgp extcommunity-list 1234 seq 5 permit admin
```

That leads to incorrect rendering, even more the line can't be deleted.

With this fix we treat numbered community-list only if it's inside the range
1-500, otherwise it's a non-numbered clist.

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>