Bluetooth: SMP: Support Pairing Request over BR/EDR

This allows to handle Pairing Request and reply with Pairing Response.

> ACL Data RX: Handle 11 flags 0x02 dlen 11
      BR/EDR SMP: Pairing Request (0x01) len 6
        IO capability: DisplayOnly (0x00)
        OOB data: Authentication data not present (0x00)
        Authentication requirement: No bonding, No MITM, Legacy,
                                    No Keypresses (0x00)
        Max encryption key size: 16
        Initiator key distribution: IdKey (0x02)
        Responder key distribution: IdKey (0x02)
< ACL Data TX: Handle 11 flags 0x00 dlen 11
      BR/EDR SMP: Pairing Response (0x02) len 6
        IO capability: DisplayOnly (0x00)
        OOB data: Authentication data not present (0x00)
        Authentication requirement: No bonding, No MITM, Legacy,
                                    No Keypresses (0x00)
        Max encryption key size: 16
        Initiator key distribution: IdKey (0x02)
        Responder key distribution: IdKey (0x02)

Jira: ZEP-605

Change-Id: I886c8d345b87dafae93d692ab39b7f1214bff733
Signed-off-by: Szymon Janc <ext.szymon.janc@tieto.com>