app/testpmd: add actions to modify TCP header fields

app/testpmd: add actions to modify TCP header fields

Add actions:
- INC_TCP_SEQ - Increase sequence number in the outermost TCP header.
- DEC_TCP_SEQ - Decrease sequence number in the outermost TCP header.
- INC_TCP_ACK - Increase acknowledgment number in the outermost TCP
                header.
- DEC_TCP_ACK - Decrease acknowledgment number in the outermost TCP
                header.

Original work by Xiaoyu Min.

This patch uses the new approach introduced by [1], using a new
macro ARG_ENTRY_HTON to pass a single integer argument to each of
the new actions.

[1] http://patches.dpdk.org/patch/55882/

Signed-off-by: Dekel Peled <dekelp@mellanox.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Acked-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>