app/testpmd: add commands for conntrack

app/testpmd: add commands for conntrack

The command line for testing connection tracking is added. To create
a conntrack object, 3 parts are needed.
  set conntrack com peer ...
  set conntrack orig scale ...
  set conntrack rply scale ...
This will create a full conntrack action structure for the indirect
action. After the indirect action handle of "conntrack" created, it
could be used in the flow creation. Before updating, the same
structure is also needed together with the update command
"conntrack_update" to update the "dir" or "ctx".

After the flow with conntrack action created, the packet should jump
to the next flow for the result checking with conntrack item. The
state is defined with bits and a valid combination could be
supported.

Signed-off-by: Bing Zhao <bingz@nvidia.com>
Acked-by: Ori Kam <orika@nvidia.com>