app/testpmd: fix port topology in RSS forward config

app/testpmd: fix port topology in RSS forward config

The testpmd user can configure port topology mode to define the port
topology between the testpmd forward ports(paired, chained and loop).

When multi-queue ports are configured by the user, the testpmd
streams are created by rss_fwd_config_setup() function, this function
doesn't take into account the chained topology mode and configures the
forward streams with paired topology mode in this case.

Configure the stream Tx port by dedicated function which calculates
a valid Tx port index as a function of the topology mode and the Rx
port index.

Fixes: af75078 ("first public release")
Cc: stable@dpdk.org
Signed-off-by: Matan Azrad <matan@mellanox.com>