app/testpmd: fix PPPoE flow command

app/testpmd: fix PPPoE flow command

The command line to create RTE flow for specific proto_id of PPPOES can
not work.

It was:
testpmd> flow create 0 ingress pattern proto_id
 proto_id [TOKEN]: match PPPoE session protocol identifier
testpmd> flow create 0 ingress pattern proto_id proto_id
 proto_id [TOKEN]: match PPPoE session protocol identifier
testpmd> flow create 0 ingress pattern proto_id proto_id proto_id
 proto_id [TOKEN]: match PPPoE session protocol identifier

The proto_id can not be set with previous implementation.

This patch is to fix this issue, and change the command line to:
testpmd> flow create 0 pattern pppoe_proto_id is xxxx

Fixes: 226c6e60c35b ("ethdev: add PPPoE to flow API")
Cc: stable@dpdk.org
Signed-off-by: Xiao Zhang <xiao.zhang@intel.com>
Acked-by: Ori Kam <orika@mellanox.com>