[PATCH 2/2] nvmet: Add port transport active flag

[Sagi Grimberg]

> tractive port flag means that nvmet transport is active and ready for
> receiving requests from host.
> It differ from enabled port state (port with subsystem symbolic link)
> which doesn't guarantee this.
> The tractive flag is necessary in case the physical ports become down
> while nvmet ports are enabled.
> In this case the port state remains enabled but tractive flag becomes false.
> 
> The tractive flag will help the administrator to monitor the port state
> from transport point of view.
> The commit also add the ability to activate the port by simply writing
> to tractive at the configfs.
> e.g.: echo 1 > config/nvmet/ports/1/tractive

Why this is a write-able variable? this is a state. I would rename it
to be trstate.