kprobes: Fix check for probe enabled in kill_kprobe()

In the Linux kernel, the following vulnerability has been resolved:

kprobes: Fix check for probe enabled in kill_kprobe()

In kill_kprobe(), the check whether disarm_kprobe_ftrace() needs to be

called always fails. This is because before that we set the

KPROBE_FLAG_GONE flag for kprobe so that "!kprobe_disabled(p)" is always

false.

The disarm_kprobe_ftrace() call introduced by commit:

0cb2f1372baa ("kprobes: Fix NULL pointer dereference at kprobe_ftrace_handler")

to fix the NULL pointer reference problem. When the probe is enabled, if

we do not disarm it, this problem still exists.

Fix it by putting the probe enabled check before setting the

KPROBE_FLAG_GONE flag.