swarm: rate limit establishing new connections

[magik6k]

I'm on a new internet connection since a few weeks and I'm noticing interesting pattern with the ISP provided router - it can handle 1000s of connections just fine, but whenever I try to establish 100+ connections is a really short time (around 1 connection/ms), it just freezes for a few seconds or just dies (same with closing connections, but that's an issue for connmgr).

[magik6k]

Note that this should be optional as it may impact DHT performance quite a bit

[Stebalien]

Interesting... We should also be able to use relays without killing the DHT too much but the problem there is:

1. Picking the relay.
2. Not killing the relay.
3. Switching away from the relay for, e.g., bitswap.

---

Note: This could also be due to the number of connection attempts we make. We should probably limit the number of dials we attempt per peer to, e.g., 10-20 at most.

[raulk]

We now have a dial pacer in the DHT: libp2p/go-libp2p-kad-dht#237.