Suppress 'zfs receive' memory warning

As part of zfs_ioc_recv() a zfs_cmd_t is allocated in the kernel
which is 17808 bytes in size.  This sort of thing in general should
be avoided.  However, since this should be an infrequent event for
now we allow it and simply suppress the warning with the KM_NODEBUG
flag.  This can be revisited latter if/when it becomes an issue.

Closes openzfs#178

module/zfs/zfs_ioctl.c

@@ -3455,7 +3455,7 @@ zfs_check_clearable(char *dataset, nvlist_t *props, nvlist_t **errlist)
 
 	VERIFY(nvlist_alloc(&errors, NV_UNIQUE_NAME, KM_SLEEP) == 0);
 
-	zc = kmem_alloc(sizeof (zfs_cmd_t), KM_SLEEP);
+	zc = kmem_alloc(sizeof (zfs_cmd_t), KM_SLEEP | KM_NODEBUG);
 	(void) strcpy(zc->zc_name, dataset);
 	pair = nvlist_next_nvpair(props, NULL);
 	while (pair != NULL) {