luci-mod-status: handle ct helpers in nftables

luci-mod-status: handle ct helpers in nftables

These appear when modules such as the following are installed:
-kmod-nf-nathelper
-kmod-nf-nathelper-extra

They render as e.g.:

 Utilise *ftp* conntrack helper

when fw4 rules similar to the following exist

```
table inet fw4 {
        chain helper_lan {
                tcp dport 21 ct helper set "ftp" comment "!fw4: FTP passive connection tracking"
        }
}
```

ht @dave14305 for the working code diff

Signed-off-by: Paul Donald <[email protected]>