conntrack: Add 'dl_type' parameter to conntrack_execute().

conntrack: Add 'dl_type' parameter to conntrack_execute().

Now that dpif_execute has a 'flow' member, it's pretty easy to access a
the flow (or the matching megaflow) in dp_execute_cb().

This means that's not necessary anymore for the connection tracker to
reextract 'dl_type' from the packet, it can be passed as a parameter.

This change means that we have to complicate sightly test-conntrack to
group the packets by dl_type before passing them to the connection
tracker.

Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>
Acked-by: Joe Stringer <joe@ovn.org>