security/sshguard: Update to 1.6.4

• Add PID file support back to rc script
• Rename some rc script parameters to better align with sshguard(8)
  
  sshguard_safety_thresh -> sshguard_danger_thresh sshguard_pardon_min_interval -> sshguard_release_interval sshguard_prescribe_interval -> sshguard_reset_interval

Release notes:

This release brings updated signatures, usability improvements, and bug
fixes. Highlights in this release include:

• Match Postfix pre-authentication disconnects
• Fix bashisms in iptables backend
• Fix size argument in inet_ntop() call
• Remove excessive logging when polling from files
• Keep looking for unreadable files while polling
• Update Dovecot signature for POP3
• Match "Connection reset" message for SSH
• Resurrect PID file option by popular demand
• Adjust default abuse threshold

Most notably, some default options have changed. The abuse threshold has
been reduced to 30 (3 attacks) and the initial block time has been
lowered to 2 minutes (from 7). These settings can be overridden from the
command line. Package maintainers should check their scripts.

The PID file option (-p) has been resurrected.