net: Collect net_pkt TX timing statistics when passing IP stack

Collect information how long net_pkt has travelled in IP stack
in certain points. See network documentation what these points
are and how to get information about the timings. This initial
commit adds support to TX timing collection.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
7 files changed