Bluetooth: Add toggle to switch off interleave scan

This patch add a configurable parameter to switch off the interleave
scan feature.

Signed-off-by: Howard Chung <howardchung@google.com>
Reviewed-by: Alain Michaud <alainm@chromium.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>