"port X" can be specified without "protocol"

The following is accepting by husk as valid, however rejected by netfilter due to "protocol" missing (port is only valid with protocol TCP or UDP)

```
accept destination address foobar.example.com port 123
```

Should be one of:

```
accept destination address foobar.example.com protocol tcp port 123
accept destination address foobar.example.com protocol udp port 123
```
