stm32/nimble_hci_uart.c: Prevent scheduler running during CYW-BT wakeup.
stm32/nimble_hci_uart.c: Prevent scheduler running during CYW-BT wakeup.

Using mp_hal_delay_ms allows the scheduler to run, which might result in
another transmit operation happening, which would bypass the sleep (and
fail).  Use mp_hal_delay_us instead.

pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython