Bug#969207: Iptables/netbase dependency in backports makes ebtables uninstallable

[ryan]

Package: iptables
Version: 1.8.5-3~bpo10+1

Installing iptables (1.8.5-3~bpo10+1) pulls in netbase > 6. This version 
of netbase has a dependency on ebtables that is not present in 
backports, and this therefore makes ebtables uninstallable.

This breaks some pretty important software (eg recent versions of 
kubernetes)