trelay: use struct_size helper in allocation

Makes it clear that the allocation is dealing with a flex array member.

Signed-off-by: Rosen Penev <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/21960
Signed-off-by: Robert Marko <[email protected]>

package/kernel/trelay/src/trelay.c

@@ -152,7 +152,7 @@ static int trelay_do_add(char *name, char *devn1, char *devn2)
 	struct trelay *tr, *tr1;
 	int ret;
 
-	tr = kzalloc(sizeof(*tr) + strlen(name) + 1, GFP_KERNEL);
+	tr = kzalloc(struct_size(tr, name, strlen(name) + 1), GFP_KERNEL);
 	if (!tr)
 		return -ENOMEM;