Bus 1 transceiver is kept active while car is off

We only use bus 0/transceiver 1/3 for CAN ignition, so bus 1/transceiver 2 is kept up needlessly. The [power save mode is set correctly](https://github.com/commaai/panda/blob/edf042883ebcf958d63cb7337d816edb50b50168/board/boards/red_chiplet.h#L30-L40), but setting the [safety mode to SILENT or NOOUTPUT](https://github.com/commaai/panda/blob/edf042883ebcf958d63cb7337d816edb50b50168/board/main.c#L87) calls `set_can_mode` which [disables and re-enables transceivers 2 and 4 to configure them](https://github.com/commaai/panda/blob/edf042883ebcf958d63cb7337d816edb50b50168/board/boards/red_chiplet.h#L42-L82) without checking the power save mode.

Do we care about this? We may want to use bus 1 in the future while the car is off, but right now we don't.