Accept but ignore TASKQ_DC_BATCH and TQ_FRONT

For the moment the SPL accepts the TASKQ_DC_BATCH and TQ_FRONT
flags however they get silently ignored.  This is harmless for
the moment but it does need to be implemented at some point.

include/sys/taskq.h

@@ -39,6 +39,7 @@
 #define TASKQ_CPR_SAFE          0x00000002
 #define TASKQ_DYNAMIC           0x00000004
 #define TASKQ_THREADS_CPU_PCT   0x00000008
+#define TASKQ_DC_BATCH          0x00000010
 
 typedef unsigned long taskqid_t;
 typedef void (task_func_t)(void *);
@@ -53,6 +54,7 @@ typedef void (task_func_t)(void *);
 #define TQ_NOQUEUE              0x01000000
 #define TQ_NOALLOC              0x02000000
 #define TQ_NEW                  0x04000000
+#define TQ_FRONT                0x08000000
 #define TQ_ACTIVE               0x80000000
 
 typedef struct taskq {