network: a different implementation of *un*setting firewalld zone when network is...

network: a different implementation of *un*setting firewalld zone when network is destroyed

(this is a remake of commit v10.7.0-78-g200f60b2e1, which was reverted
due to a regression in another patch it was dependent on. The new
implementation just adds the call to virFirewallDInterfaceUnsetZone()
into the existing networkRemoveFirewallRules() (but only if we had set
a zone when the network was first started).

Replaces: 200f60b2e12e68d618f6d59f0173bb507b678838
Resolves: https://issues.redhat.com/browse/RHEL-61576
Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Jiri Denemark <jdenemar@redhat.com>