iptables cannot correctly handle situations when more than one command
is trying to set netfilter rules. In such situations, iptables may fail
with EAGAIN, which results in iptables: Unknown error
18446744073709551615.
Such situation can easily happen when multiple network devices are
configured for a domain as vif hotplug scripts are called in parallel
for all of the network devices.
Signed-off-by: Jiri Denemark <jdenemar@redhat.com>