serial_arduino.c: Use if() instead of #if

This tests that both branches are valid code on every compilation.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Add a bunch more debug variables

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Use 57600 baud instead of 115200 baud

Some of the new boards can't read 115200 reliably.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>