[SCSI] libiscsi: regression: fix header digest errors

This fixes a regression introduced with this commit:

commit d3305f34
Author: Mike Christie <michaelc@cs.wisc.edu>
Date:   Thu Aug 20 15:10:58 2009 -0500

    [SCSI] libiscsi: don't increment cmdsn if cmd is not sent

in 2.6.32.

When I moved the hdr->cmdsn after init_task, I added
a bug when header digests are used. The problem is
that the LLD may calculate the header digest in init_task,
so if we then set the cmdsn after the init_task call we
change what the digest will be calculated by the target.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Cc: Stable Tree <stable@kernel.org>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>