If we call lxc-freeze multiple times for an already frozen container, LXC
triggers useless freezing by writing into the "freezer.state" cgroup file.
This is the same when we call lxc-unfreeze multiple times.
Checking the current state with a LXC_CMD_GET_STATE
(calling c->state) would permit to check if the container is FROZEN
or not.
Signed-off-by: Rachid Koucha <rachid.koucha@gmail.com>