raw: replace hard coded constants by MAC_LEN

Signed-off-by: Jiri Benc <jbenc@redhat.com>
raw: separate src and dst addresses

In order to be able to convert to a generic address struct, separate source
and destination address into separate fields.

Signed-off-by: Jiri Benc <jbenc@redhat.com>
Let transport_recv/send/peer use ptp_message

The callers of those functions are all using ptp_message. As we're going to
return more information (the address), let those functions just fill in the
ptp_message fields directly.

Some minor reshuffling needed to prevent circular header dependencies.

Signed-off-by: Jiri Benc <jbenc@redhat.com>