Bluetooth: Add secure flag for mgmt_pin_code_req

Extend the mgmt_pin_code_request interface to require secure
pin code (16 digit) for authentication.

This is a kernel part of the secure pin code requirement notification
to user space agent.

Code styling fix by Johan Hedberg.

Signed-off-by: Waldemar Rymarkiewicz <waldemar.rymarkiewicz@tieto.com>
Signed-off-by: Johan Hedberg <johan.hedberg@nokia.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>