Unbreak creating etherstubs on SmartOS
Unbreak creating etherstubs on SmartOS

SmartOS (no longer?) handles setting an MTU for etherstub devices,
so silently drop it in order to maintain the current API.

salt:2066 salt % doas salt-ssh smartos-gz nictagadm.add storage0 etherstub
smartos-gz:
    ----------
    Error:
        Error: Cannot specify MTU for local nic tag

Also fixup two examples while here which failed to run and use
format() in a consistent manner.

Tested on SmartOS 20160204T080230Z and 20180203T031130Z

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt