Bluetooth: Interleaved discovery support

This patch adds interleaved discovery support to MGMT Start
Discovery command.

In case interleaved discovery is not supported (not a dual mode
device), we perform BR/EDR or LE-only discovery according to the
device capabilities.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>