[SCSI] libsas: introduce scmd_dbg() to quiet false positive "timeout" messages

[SCSI] libsas: introduce scmd_dbg() to quiet false positive "timeout" messages

libsas sometimes short circuits timeouts to force commands into error
recovery.  It is misleading to log that the command timed-out in
sas_scsi_timed_out() when in fact it was just queued for error handling.
It's also redundant in the case of a true timeout as libata eh will
detect and report timeouts via it's AC_ERR_TIMEOUT facility.

Given that some environments consider "timeout" errors to be indicative
of impending device failure demote the sas_scsi_timed_out() timeout
message to be disabled by default.  This parallels ata_scsi_timed_out().

[jejb: checkpatch fix]
Reported-by: Xun Ni <[email protected]>
Tested-by: Nelson Cheng <[email protected]>
Acked-by: Lukasz Dorau <[email protected]>
Signed-off-by: Dan Williams <[email protected]>
Signed-off-by: James Bottomley <[email protected]>