In case of pre v2.1 devices authentication request will return
success immediately if the link key already exists without any
authentication process.

That means, it's not possible to re-authenticate the link if you
already have combination key and for instance want to re-authenticate
to get the high security (use 16 digit pin).

Therefore, it's necessary to check security requirements on auth
complete event to prevent not enough secure connection.
Signed-off-by: Waldemar Rymarkiewicz <waldemar.rymarkiewicz@tieto.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>