Fix the interrupt mitigation stuff, now that I know what's going on.

• If the RX mitigation interrupts fire, set HAL_INT_RX and clear the relevant underlying interrupt(s) as well.

• If the TX mitigation interrupts fire, set HAL_INT_TX

• If any of the TX status bits (ok, err, desc, eol) are set, update the TX bitmask, but don't set HAL_INT_TX if TX interrupt mitigation is enabled.