add support for shorter connection intervals

[J0hannes101]

Adds support for ble 6.2 shorter connection intervals

I tested this using this example i wrote

Frame space updates, and reading the Minimum Supported Connection Interval works as expected. However, setting the default rate parameters and requesting a connection rate fail with these errors:

• Unsupported LMP Parameter Value / Unsupported LL Parameter Value (for set_default_connection_rate_parameters)
• Unsupported Remote Feature (for request_connection_rate)

Testing was done with two nRF52840 devices. According to the Nordic example, the feature should be supported, but the LE command mask reports it as unsupported.

At this point, I'm unclear whether something is missing in trouble, nrf-sdc, bt-hci, my application just being wrong or if the nRF52840 does not fully support this feature.

Note:

• also needs new version of bt-hci for cargo

[lulf]

Thanks, it looks good. Once bt-hci is released I'd be happy to merge this. You may also need to update nrf-sdc to enable the required supported features to get it working.