This change is based on Linux commit 40630f462824ee.
csio.resid should account for transfer_len only for success and
SRB_STATUS_DATA_OVERRUN condition.
I am not sure how exactly this change works, but I have a report from a user
that they see lots of checksum errors when running a pool scrub concurrently
with iozone -l 1 -s 100G. After applying this patch the problem cannot be
reproduced.