IB/iser: Allow bind only when connection state is UP

We need to fail the bind operation if the iser connection state != UP
(started teardown) and this should be done under the state lock.

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>