Description of problem:
restarting firewalld.service resultes in more rules every restart, eventually slowing the system.

Version-Release number of selected component (if applicable):
First began in firewalld 0.8.0-4 and confirmed through

How reproducible:
Easily on an RHEL system with firewalld 0.8.0-4 or newer.

Steps to Reproduce:
1. Install firewalld 0.8.0-4 or newer.
2. Set CleanUpOnExit=no in /etc/firewalld/firewalld.conf
3. systemctl restart firewalld ### to make new setting effective
4. nft list ruleset | wc -l
5. systemctl restart firewalld
6. nft list ruleset | wc -l

Actual results:
After ever restart the ruleset grows

Expected results:
After restart of firewalld.service ruleset does not grow.

Additional info:
firewall-cmd --reload, or systemctl reload firewalld, which send SIGHUP instead of stop/start firewalld, the ruleset does not grow even with FlushAllOnReload=no:

FlushAllOnReload=no:

1. nft list ruleset | wc -l
   528
2. firewall-cmd --reload
   success
3. nft list ruleset | wc -l
   528

Customer uses CleanUpOnExit=no to avoid all windows where firewall rules might not exist.