apparmor: ensure unconfined profiles have dfas initialized

Generally unconfined has early bailout tests and does not need the
dfas initialized, however if an early bailout test is ever missed
it will result in an oops.

Be defensive and initialize the unconfined profile to have null dfas
(no permission) so if an early bailout test is missed we fail
closed (no perms granted) instead of oopsing.

Signed-off-by: John Johansen <john.johansen@canonical.com>