fork: add kernel-doc for clone3

Add kernel-doc for the clone3() syscall.

Link: https://lore.kernel.org/r/20191001114701.24661-2-christian.brauner@ubuntu.com
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

kernel/fork.c

@@ -2604,6 +2604,17 @@ static bool clone3_args_valid(const struct kernel_clone_args *kargs)
 	return true;
 }
 
+/**
+ * clone3 - create a new process with specific properties
+ * @uargs: argument structure
+ * @size:  size of @uargs
+ *
+ * clone3() is the extensible successor to clone()/clone2().
+ * It takes a struct as argument that is versioned by its size.
+ *
+ * Return: On success, a positive PID for the child process.
+ *         On error, a negative errno number.
+ */
 SYSCALL_DEFINE2(clone3, struct clone_args __user *, uargs, size_t, size)
 {
 	int err;