[SCSI] fcoe: Change fcoe receive thread nice value from 19 (lowest priority) to -20

This change makes the fcoe Rx threads have the same nice value
as lpfc and qla2xxx Rx threads.

Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>