apply xnu thread policies to taskq_d threads too

assuming this works, it calls out for DRY refactoring
with the other two flavours, that operate on current_thread().

module/os/macos/spl/spl-taskq.c

@@ -2711,6 +2711,44 @@ taskq_bucket_extend(void *arg)
 	tqe->tqent_thread = (kthread_t *)0xCEDEC0DE;
 	thread = thread_create(NULL, 0, (void (*)(void *))taskq_d_thread,
 	    tqe, 0, pp0, TS_RUN, tq->tq_pri);
+
+	thread_precedence_policy_data_t prec = { 0 };
+	prec.importance = tq->tq_pri - 81;
+               if (tq->tq_DC <= 50)
+                       prec.importance--;
+               if (tq->tq_flags & TASKQ_DC_BATCH)
+                       prec.importance--;
+	       if (prec.importance < -11)
+		       prec.importance = -11;
+	       else if (prec.importance > -1)
+		       prec.importance = -1;
+               kern_return_t precret = thread_policy_set(tqe->tqent_thread,
+                   THREAD_PRECEDENCE_POLICY,
+                   (thread_policy_t)&prec,
+                   THREAD_PRECEDENCE_POLICY_COUNT);
+               if (precret != KERN_SUCCESS) {
+                       printf("SPL: %s:%d: WARNING failed to set thread precedence retval %d"
+                           " (prec now %d)\n",
+                           __func__, __LINE__, precret, prec.importance);
+               } else {
+                       tq->tq_pri = defclsyspri + prec.importance;
+                       dprintf("SPL: %s:%d: SUCCESS setting thread precedence %x, %s\n", __func__, __LINE__,
+                           prec.importance, tq->tq_name);
+               }
+
+               /* set the TIMESHARE property on all taskq_d threads */
+               thread_extended_policy_data_t policy = { .timeshare = TRUE };
+               kern_return_t kret = thread_policy_set(tqe->tqent_thread,
+                   THREAD_EXTENDED_POLICY,
+                   (thread_policy_t)&policy,
+                   THREAD_EXTENDED_POLICY_COUNT);
+               if (kret != KERN_SUCCESS) {
+                       printf("SPL: %s:%d: WARNING failed to set timeshare policy retval: %d, %s\n",
+                           __func__, __LINE__, kret, tq->tq_name);
+               } else {
+                       dprintf("SPL: %s:%d: SUCCESS setting timeshare policy, %s\n", __func__, __LINE__,
+                           tq->tq_name);
+               }
 #else
 
 	/*