community/docker: fix race condition between docker and iptables

When the system is booting, the order of docker and iptables was not
specified due to the missing dependency. That could lead to docker
setting up the chains and iptables wiping them clean if the order of
start was 1. docker 2. iptables.

Explicit dependency should make that working correctly.
7 jobs for !20900 with docker in 7 seconds
merge request