Bluetooth: Add automated SSP user confirmation responses

This patch adds automated negative and positive (auto-accept) responses
for Secure Simple Pairing user confirmation requests. The responses are
only sent if the HCI_MGMT flag is set in order not to confuse older user
space versions (without management interface support).

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