tests: Add test-conntrack pcap test.

tests: Add test-conntrack pcap test.

Simple program that runs the packet in a pcap file through the
connection tracker and prints the 'ct_state' for each packet.

E.g. the line:

`./test/ovstest test-conntrack capture.pcap 2`

sends the packets in `capture.pcap` to the connection tracker, 2 per
call.

Useful for debugging.

Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>
Acked-by: Flavio Leitner <fbl@sysclose.org>