fail2ban 0.9 branch does not support IPv6; existing logic can misinterpret IPv6 addresses in logs

[Markus Ueberall]

See release note for v0.9.5 (https://github.com/fail2ban/fail2ban/releases) -- either the 0.10.x branch should be packaged or available patches (e.g., published at https://crycode.de/wiki/Fail2Ban) should be adopted.

NB this is *not* just a "feature request"--the existing code can wrongly ban IPv4 addresses by misinterpreting IPv6 addresses in the logs. So at the very least, IPv6 addresses should *never* lead to spurious bans:

# grep failregex /etc/fail2ban/filter.d/seafile-auth.conf
failregex = Login attempt limit reached.*, ip: <HOST>
# grep eumel /var/www/apps/seafile/logs/seahub.log
2016-07-30 12:06:39,595 [WARNING] seahub.auth.views:191 login Login attempt limit reached, show Captcha, email/username: eumel, ip: nnnn:nnnn:nnnn:nnnn:nnnn:nnnn:nnnn:nnnn, attemps: 5
# fail2ban-client status seafile
Status for the jail: seafile
|- Filter
| |- Currently failed: 1
| |- Total failed: 3
| `- File list: /var/www/apps/seafile/logs/seahub.log
`- Actions
   |- Currently banned: 1
   |- Total banned: 1
   `- Banned IP list: 0.0.7.209

[Markus Ueberall (ueberall)]

Reported upstream as well (https://github.com/fail2ban/fail2ban/issues/1493)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.