Review DiscoveryConfig defaults and values

[cskiraly]

In test DiscoveryConfig is set to DiscoveryConfig.init(1000, 24, 5)
https://github.com/codex-storage/nim-libp2p-dht/blob/4375b9229815c332a3b1a9d0091d5cf5a74adb2e/tests/dht/test_helper.nim#L34

This calls
https://github.com/codex-storage/nim-libp2p-dht/blob/4375b9229815c332a3b1a9d0091d5cf5a74adb2e/libp2pdht/private/eth/p2p/discoveryv5/protocol.nim#L1013-L1017

Which sets tableIpLimit, bucketIpLimit, bitsPerHop. Default values should be reviewed for tests and for deployment.

[cskiraly]

@benbierens, bucketIpLimit might be influencing your tests.