trace: disable port number conversion in tcpdump mode

tcpdump port number conversions vary from system to system. Turn of the
conversions to have consistent output which is also simpler to assert
for in tests.

Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>