This adds the request handler of MGMT_OP_ADD_ADV_PATTERNS_MONITOR command.
Note that the controller-based monitoring is not yet in place. This tracks
the content of the monitor without sending HCI traffic, so the request
returns immediately.

The following manual test was performed.
- Issue btmgmt advmon-add with valid and invalid inputs.
- Issue btmgmt advmon-add more the allowed number of monitors.
Signed-off-by: Miao-chen Chou <mcchou@chromium.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>