iscsi-target: Avoid rejecting incorrect ITT for Data-Out

This patch changes iscsit_check_dataout_hdr() to dump the incoming
Data-Out payload when the received ITT is not associated with a
WRITE, instead of calling iscsit_reject_cmd() for the non WRITE
ITT descriptor.

This addresses a bug where an initiator sending an Data-Out for
an ITT associated with a READ would end up generating a reject
for the READ, eventually resulting in list corruption.

Reported-by: Santosh Kulkarni <santosh.kulkarni@calsoftinc.com>
Reported-by: Arshad Hussain <arshad.hussain@calsoftinc.com>
Cc: stable@vger.kernel.org # 3.10+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>