Note that this slightly breaks backward compatibility when
Termination=1. Previously, this is handled as boolean true, then 120 ohm
was used. But now with this commit, it is handled as 1 ohm.
For now, this function is nearly equivalent to the si_uint64 parser, except for
an additional range check as Linux only takes 32-bit values as bitrates. In
future, this may also be used to introduce fancier bitrate config formats.
Yu Watanabe
Richard Petri