Peer banning not enabled by default, no manual blacklist option

[anthonyhseb]

I had my node fall out of sync and not recover because of a couple of bad peers that were sending me bad block data. I found no blacklist option in the configuration file, and automatic banning was disabled by default.

Enabling automatic banning solved my issue, but only after being out of service for a few hours.

If banning is disabled by default, many people operating nodes could have their node DoS'ed by other bad nodes.