app/testpmd: fix typo in comment
app/testpmd: fix typo in comment

Correct minor typing mistake:
then ==> the

Fixes: 79bec05b32b7 ("app/testpmd: add ability to split outgoing packets")
Cc: stable@dpdk.org

Signed-off-by: Dekel Peled <f1921780d3213ef78965aec36396441d9bf8894c@mellanox.com>
Acked-by: Bernard Iremonger <233eeff376ad0c06f66f06c5522ea3c4feb30d3b@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk