update ipns reference to libp2p dht config

[Qmstream]

The ipns initialization is checking the wrong path to the libp2p's dht config flag, and as result it always boots in the offline state.

The following code should print the enabled routers:

const config = {EXPERIMENTAL:{dht:true}, libp2p:{config:{dht:{enabled:true}}}}
const ipfs = new Ipfs(config)
ipfs.on('ready', () => console.log(ipfs._ipns.routing.stores))

With the patch the ipfs.libp2p.dht datastore is used.

[alanshaw]

Thanks @Qmstream