Check and log the default pretimeout governor configured in the kernel.
The pretimeout will not work unless at least one governor is available
and configured. This requires loading a kernel module manually.
Since version 4.5, the max possible timeout is UINT_MAX / 1000 since it
does calculations in milliseconds. A small helper function is added to
make this conversion and saturation and will be used more in the next
commit.
Also document the usage of signed integers by the kernel userspace API.
Curtis Klein