This commit has no technical effect: what works still works, and what
doesn't work still doesn't work.  Still, the inlines will do
type-checking at a later time when we have a structure for the ptp
header.

Moreover the renames allow me to trace all uses in order to change
them; it also generates build errors in wrpc-sw, forcing me to fix the new
use in there as well, when I update ppsi as submodule.
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>