New firmware fixes iSCSI problems with some LeftHand targets that don't
set TTT=0xffffffff for Data-In according to spec.  Firmware generates
exception warnings for this condition and becomes very slow.  This is
fixed by suppressing these warnings when using default error mask.

Signed-off-by: Michael Chan <[email protected]>
Signed-off-by: Ben Hutchings <[email protected]>