Bluetooth: Interleave with allowlist scan

This patch implements the interleaving between allowlist scan and
no-filter scan. It'll be used to save power when at least one monitor is
registered and at least one pending connection or one device to be
scanned for.

The durations of the allowlist scan and the no-filter scan are
controlled by MGMT command: Set Default System Configuration. The
default values are set randomly for now.

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