IB/srpt: Log out all initiators if a port is disabled

If an initiator observes LUN deletion during shutdown of the
target stack then that will trigger an I/O error even when using
multipathd. Users need a way to avoid that shutting down the
target stack causes I/O errors, e.g. by providing a way to force
initiator logout. Hence close all sessions if a target port is
disabled.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Estrin <alex.estrin@intel.com>
Cc: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>