examples/l3fwd-power: check packet types after start

examples/l3fwd-power: check packet types after start

l3fwd-power uses `--parse-ptype' parameter to query egress packets
type.  Before that feature is enabled l3fwd-power verifies PMD ability
to advertise supported packet types with
rte_eth_dev_get_supported_ptypes().

The above ethdev function API contains this note:
"
Better to invoke this API after the device is already started or rx burst
function is decided, to obtain correct supported ptypes.
"

The patch updates code for PMDs that register supported types after
dev_start.

Fixes: 82bea4661626 ("examples/l3fwd-power: add --parse-ptype option")
Cc: stable@dpdk.org
Signed-off-by: Gregory Etelson <getelson@nvidia.com>