Backtrace generated by firewall-cmd when NetworkManager cannot set interface ZONE because of rule file

Issue

• firewall-cmd prints a backtrace which triggers abrt when trying to set the zone of an interface in RHEL 7.3+:

  [root@rhel73test ~]# firewall-cmd --permanent --zone=external --add-interface=eth0
  The interface is under control of NetworkManager, setting zone to 'external'.
  Traceback (most recent call last):
    File "/usr/bin/firewall-cmd", line 1585, in <module>
      if not try_set_zone_of_interface(a.zone, interface):
    File "/usr/bin/firewall-cmd", line 424, in try_set_zone_of_interface
      nm_set_zone_of_connection(_zone, connection)
    File "/usr/lib/python2.7/site-packages/firewall/core/fw_nm.py", line 99, in nm_set_zone_of_connection
      con.commit_changes(True, None)
  GLib.Error: nm-settings-error-quark: Cannot modify a connection that has an associated 'rule-' or 'rule6-' file (0)