MTU exchange happens before pairing, causing peripherals to disconnect

[fede2cr]

I haven't tested backporting this against released versions, will try to backport if devs agree it makes sense

I'm building a circuitpython library to talk with commercial "guitar" pedals (Valeton GP-5, Sonicake Smart Box so far) over BLE, to control them with cpy pedalboards. With both I get disconnect errors while trying to pair with them.

This patch changes the order, so that SMP security is initiated before MTU exchange, this allows the devices to pair properly.

Tested only in esp32-s3 qt with these two devices, not sure if it breaks pairing with other BLE devices.

[tannewt]

Are we violating the bluetooth spec or just confusing these pedals?

[fede2cr]

I don't know enough about ble spec to know if it was currently broken. I think this patch can be described as a compatibility workaround for these devices, or as a parity patch, in the sense that the Chocotone which is a similar pedal-control software but based in c++ (arduino esp32 code v3.1.2) does negotiation in this way, which is what I used to understand and sniff why circuitpython wasn't connecting with this devices.