netcmd: silo command uses more consistent naming for tgt args

netcmd: silo command uses more consistent naming for tgt args

The args --user-tgt-lifetime-mins, --service-tgt-lifetime-mins and
--computer-tgt-lifetime-mins suffixed with -mins to be consistent
with Windows tooling.

For these, the internal names don't need to change and neither do
the model fields, only the external cli interface has this.

Signed-off-by: Rob van der Linde <rob@catalyst.net.nz>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>