[SCSI] iscsi: fix iscsi_endpoint leak

When iscsid restarts it does not know the connection's
endpoint, so it is getting leaked. This fixes the problem
by having the iscsi class force a disconnect before a
new connection is bound.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>