Bluetooth: Fix L2CAP security check

With older userspace versions (using hciops) it might not have the
key type to check if the key has sufficient security for any security
level so it is necessary to check the return of hci_conn_auth to make
sure the connection is authenticated

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Acked-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>