swarm: enable p2p/discovery and disable dynamic dialling

[nonsense]

This PR is re-enabling p2p discovery, but disabling the dynamic dialling functionality - the reason why we didn't want to have the p2p discovery in the first place.

The reason for this is - the hive protocol and the Kademlia table implementation on Swarm side does not update the underlay addresses of peers. More specifically Kademlia.Register does not update the underlay addresses ever, but Kademlia.On and Kademlia.Off do. This means that sometimes we are left with outdated destinations for nodes in our state store.

The p2p package handles that with:

    err := t.dial(srv, t.dest)
    if err != nil {
        log.Trace("Dial error", "task", t, "err", err)
        // Try resolving the ID of static nodes if dialing failed.
        if _, ok := err.(*dialError); ok && t.flags&staticDialedConn != 0 {
            if t.resolve(srv) {
                t.dial(srv, t.dest)
            }
        }
    }

Namely, if dialling fails, it tries to resolve an up-to-date destination for the node - something that is only done when discovery is enabled.

Bottom line: hive protocol relies heavily on the discovery functionality in the p2p package, so for now it is not wise to disable discovery on p2p.

Addresses: ethersphere/swarm#1268

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I also considered solving this directly on Swarm side, but the hive protocol implementation is not straight-forward and it is not clear how to determine what an up-to-date / accurate node destination is. What happens is that when a new node starts up and loads an out-dated node destination, it might receive a hive message with a different destination for a given node, and it can't determine which one is correct, without trying them both. We don't have functionality to do that, and implementing this seems like a major change in the hive protocol.