Bluetooth: BR/EDR: Initiate encryption on link

Adds method to start encrypting the link by local controller. Encryption
implies successful authentication to be done before.

> HCI Event: Auth Complete (0x06) plen 3
	Status: Success (0x00)
	Handle: 11
< HCI Command: Set Connection Encryption (0x01|0x0013) plen 3
	Handle: 11
	Encryption: Enabled (0x01)
> HCI Event: Command Status (0x0f) plen 4
	Set Connection Encryption (0x01|0x0013) ncmd 1
	Status: Success (0x00)
> HCI Event: Encryption Change (0x08) plen 4
	Status: Success (0x00)
	Handle: 11
	Encryption: Enabled with E0 (0x01)

Change-Id: I3bbfc6ca77a6fd088582ab45f14d7c122aec7f05
Signed-off-by: Arkadiusz Lichwa <arkadiusz.lichwa@tieto.com>