[SCSI] qla2xxx: Correct residual-count handling discrepancies during UNDERRUN handling.

For recent ISPs, software during CS_UNDERRUN handling must
determine if the two residuals, firmware-calculated and FCP_RSP,
are different to recognize if a frame has been dropped.  Update
the driver to catch this condition, and clear the
SS_RESIDUAL_UNDER and lscsi_status bits.  This logic is
consistent with what earlier firmwares did by explicitly
cracking open the FCP_RSP statuses and clearing
SS_RESIDUAL_UNDER.

Signed-off-by: Andrew Vasquez <andrew.vasquez@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>