Bluetooth: Add SMP flag to track which side is the initiator

For remotely initiated just-works pairings we want to show the user a
confirmation dialog for the pairing. However, we can only know which
side was the initiator by tracking which side sends the first Security
Request or Pairing Request PDU. This patch adds a new SMP flag to
indicate whether our side was the initiator for the pairing.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>