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 <mchan@broadcom.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>