Redact password in Stringer of `packets.ConnectPacket`

[besedad]

Return value of String() is not safe to use because it may contain unredacted password. If not careful, a password may leak out to logs and subsequently spread to other channels. I propose to modify the Stringer to replace any non-empty string with <redacted>. I'll follow up with a pull-request if the issue gets accepted.

[MattBrittan]

This is mainly intended for use when testing (and including the password could allow the user to spot an issue). Having said that I can see how this lead to the password leaking into logs so have no issue with your proposed change.