Restart fail2ban using systemd condrestart

[WilliamDEdwards]

The previous code does two things:

1. Restart fail2ban ONLY if it's running with fail2ban-client ping
2. Re-add the fail2ban chain that was removed due to the ferm restart using fail2ban-client

However, using fail2ban-client reload does not re-add the f2b-* chains for me. MRE:

~# iptables -nvL | grep f2b
   15  1124 f2b-sshd   tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            multiport dports 22
Chain f2b-sshd (1 references)
~# systemctl start ferm
~# iptables -nvL | grep f2b
~# fail2ban-client reload
OK
~# iptables -nvL | grep f2b

Restarting the fail2ban service does re-add these chains:

~# systemctl restart fail2ban
~# iptables -nvL | grep f2b
    3   236 f2b-sshd   tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            multiport dports 22
Chain f2b-sshd (1 references)

Aside from this, the current fail2ban-client ping logic can be simplified by using systemd condrestart, which restarts the service only when it's running. This does mean that this commit assumes fail2ban runs as a systemd service.

I do not use your project, so I am not interested in maintaining or updating this PR. In case losing support for non-systemd systems is unacceptable, feel free to close it.