recvd_props_mode: use a uintptr_t to stash nvlists

Avoid assuming than a uint64_t can hold a pointer.

Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Signed-off-by: Brooks Davis <brooks.davis@sri.com>
Closes #14131

lib/libzfs/libzfs_dataset.c

@@ -2087,16 +2087,16 @@ zfs_is_recvd_props_mode(zfs_handle_t *zhp)
 }
 
 static void
-zfs_set_recvd_props_mode(zfs_handle_t *zhp, uint64_t *cookie)
+zfs_set_recvd_props_mode(zfs_handle_t *zhp, uintptr_t *cookie)
 {
-	*cookie = (uint64_t)(uintptr_t)zhp->zfs_props;
+	*cookie = (uintptr_t)zhp->zfs_props;
 	zhp->zfs_props = zhp->zfs_recvd_props;
 }
 
 static void
-zfs_unset_recvd_props_mode(zfs_handle_t *zhp, uint64_t *cookie)
+zfs_unset_recvd_props_mode(zfs_handle_t *zhp, uintptr_t *cookie)
 {
-	zhp->zfs_props = (nvlist_t *)(uintptr_t)*cookie;
+	zhp->zfs_props = (nvlist_t *)*cookie;
 	*cookie = 0;
 }
 
@@ -2373,7 +2373,7 @@ zfs_prop_get_recvd(zfs_handle_t *zhp, const char *propname, char *propbuf,
 	prop = zfs_name_to_prop(propname);
 
 	if (prop != ZPROP_USERPROP) {
-		uint64_t cookie;
+		uintptr_t cookie;
 		if (!nvlist_exists(zhp->zfs_recvd_props, propname))
 			return (-1);
 		zfs_set_recvd_props_mode(zhp, &cookie);