smack: fix bug: unprivileged task can create labels

In the Linux kernel, the following vulnerability has been resolved: smack: fix bug: unprivileged task can create labels If an unprivileged task is allowed to relabel itself (/smack/relabel-self is not empty), it can freely create new labels by writing their names into own /proc/PID/attr/smack/current This occurs because do_setattr() imports the provided label in advance, before checking "relabel-self" list. This change ensures that the "relabel-self" list is checked before importing the label.