apparmor: fix invalid reference on profile->disconnected

profile->disconnected was storing an invalid reference to the
disconnected path. Fix it by duplicating the string using
aa_unpack_strdup and freeing accordingly.

Fixes: 72c8a768 ("apparmor: allow profiles to provide info to disconnected paths")
Signed-off-by: Georgia Garcia <georgia.garcia@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>