README: update trex download location
README: update trex download location

The trex server no longer supports http and
the download will fail.

There is an issue with the CA being updated,
so add the wget parameter required.

Signed-off-by: Kevin Traynor <1f46c93815774a2e602547cf1e37c682d62b566d@redhat.com>

chaudron/ovs_perf,chaudron/ovs_perf