bridge: Add an option to enable port isolation

[ormergi]

Enable bridge CNI users set port-isolation [1] on the interface.

Linux-bridge port that is set as isolated cannot communicate with other isolated ports (they can still communicate with non-isolated ports).
For example:
In case I have two containers connected over a bridge (running on the same node), I want traffic to go though a smart switch, and the switch should decide whether these containers can communicate with each other according to some restrictions or policies.

Add new option should be an addition flag, controlling whether port-isolation is set on the interface or not.
Default should be false.

[1] https://serverfault.com/questions/388544/is-it-possible-to-enable-port-isolation-on-linux-bridges/1017228#1017228