Share encryption2.mod (pbkdf2.mod) settings

[michaelortmann]

Found by: michaelortmann
Patch by: michaelortmann
Fixes: #1657

One-line summary:
Share encryption2.mod (pbkdf2.mod) settings

Additional description (if needed):
If share bots have different pbkdf2 settings, they will constantly rehash shared passwords and reshare the new hashed passwords, when a user logs in. it would be best to have the same settings in each of the share bots config files. This PR lets share hubs share their setting, so that leaf bots can override their (different) config setting with the settings they received from the hub and also log a hint to adapt the config file proper.

Test cases demonstrating functionality (if applicable):

[...]
[17:58:21] Userlist transfer complete; switched over.
[17:58:21] PBKDF2: received new pbkdf2-method from share master: sha256 -> sha512. Consider setting it in your eggdrop config file.
[17:58:21] PBKDF2: received new pbkdf2-rounds from share master: 16000 -> 31337. Consider setting it in your eggdrop config file.
[...]