delta_tx and delta_rx in the SFP information are differences from
the values in the "calibration" SFP model. Thus they are signed
not uint32_t.  Fortunately nobody used negative values so far.

I also renamed the fields, to ensure the compiler would find all uses.

The commit also syncs headers to ppsi, including the changes that
happened here but were irrelevant to there.
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>