[SCSI] iscsi_tcp: fix handling of data buffer padding

If we got the padding, data and header in different skbs,
we were not handling the padding correctly because we attributed it
to the data's skb. This resulted in the initiator reading from
pad bytes + skb offset instead of the correct offset.

If you could not connect with the open solaris target, this
will fix the lock up problem you were hitting.

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