Export symbols dsl_sync_task{_nowait}

These are needed by consumers (i.e. Lustre) who wish to perform a
callback in the syncing context.  Both a blocking and non-blocking
version are available to callers.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

module/zfs/dsl_synctask.c

@@ -174,4 +174,6 @@ dsl_sync_task_sync(dsl_sync_task_t *dst, dmu_tx_t *tx)
 }
 
 #if defined(_KERNEL) && defined(HAVE_SPL)
+EXPORT_SYMBOL(dsl_sync_task);
+EXPORT_SYMBOL(dsl_sync_task_nowait);
 #endif