Add option to disable BLE HID host advertising

[Iemooon]

Summary

Add CONFIG_ZMK_BLE_DISABLE_HOST_ADV to allow disabling BLE HID host advertising while keeping BLE enabled.

This is useful for USB dongle receiver builds that need BLE for split central communication with peripherals, but should not advertise themselves as a pairable BLE HID device to host computers.

Details

When CONFIG_ZMK_BLE_DISABLE_HOST_ADV is enabled, update_advertising() stops any active host advertising and returns without starting BLE HID advertising.

BLE itself remains enabled, so split central behavior can continue to scan for and connect to split peripherals.

Use Case

A USB dongle receiver may need to:

• communicate with split keyboard halves over BLE
• output HID reports to the host over USB
• avoid appearing as a BLE keyboard available for host pairing

This option supports that setup without requiring CONFIG_ZMK_BLE=n, which would also disable the BLE functionality needed for split communication.

Testing

Built and tested with a USB dongle receiver configuration using BLE split central communication.