Update on_next_reset for new safe mode.

[tannewt]

Fixes #1831

[dhalbert]

Tested on Hallowing. Works as expected when doing microcontroller.reset().

Q: Is it also supposed to work when pressing the reset button? It does not work for me when doing that.

If not, then would it make sense to eliminate on_next_reset() and just add an optional argument to microcontroller.reset() ?

Will re-review after answer.

[tannewt]

Will have to pick this up tomorrow. Looks like it should work with the button for CircuitPlayground single click into bootloader: #350 (comment)

[dhalbert]

Neither the BOOTLOADER nor SAFE_MODE worked when pressing the reset button once. Maybe the value is getting overwritten by the bootloader, since now it's a regular static: static mcu_runmode_t next_reset; instead of using _ezero ?

[tannewt]

@dhalbert I didn't expect it to work but I do now. :-) I swapped it back to setting values in on_next_reset.

[dhalbert]

Tested with M0 and M4 boards with pushbutton and microcontroller.reset() resets. Works great!

[dhalbert]

Tested this further on Feather nRF52840 and it doesn't change the mode when reset either by hand or programmatically.

[dhalbert]

Ah, OK, I see issue #1868 for nrf support.