This allows to uncomment the original DBGV in ptp code, until they are
turned to serious diagnostic messages. Then these two functions should
disappear, in my opinion.
Most DBGV use no arguments, so the default function is smaller; and
printf-like DBGV can be turned to DBGV_ARGS instead.
Signed-off-by: Alessandro Rubini <firstname.lastname@example.org>