This kills the global build-time macro pp_verbose_dump to use flags
instead.  In msg.c this commit fakes the old pp_verbose_dump, which
however is extracted from the global flags.

So, setting "frames" level to 2 prints information on frames being
received ("-d 002").

Until I get to integrate tools/ptpdump in the daemon itself, we have
no instance-specific dump, nor symmetric dumping of input and output.
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>