[SCSI] iscsi tcp: bidi capable

Mark iscsi_tcp as being capable of bidirectional transfers.  The
bsg interface checks this bit before attempting any bidirectional
commands.

Signed-off-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>