dracut: fix zero MAC problem when all bridge slaves get removed
This was causing sending DHCP offer from zero MAC, which did not arrive to the client. This was causing dracut_NM_bridge_eth0 test failing, when it was not the first test run.
@os:rhel8.3 @RunTests:dracut_setup,dracut_NM_NFS_root_dhcp,dracut_NM_bridge_eth0,dracut_NM_vlan_over_everything