app/testpmd: support forced ethernet speed

app/testpmd: support forced ethernet speed

Add support for forced ethernet speed setting.
Currently testpmd tries to configure the Ethernet port in autoneg mode.
It is not possible to set the Ethernet port to a specific speed while
starting testpmd. In some cases capability to configure a forced speed
for the Ethernet port during initialization may be necessary. This patch
tries to add this support.

The patch assumes full duplex setting and does not attempt to change that.
So speeds like 10M, 100M are not configurable using this method.

The command line to configure a forced speed of 10G:
dpdk-testpmd -c 0xff  -- -i  --eth-link-speed  10000

The command line to configure a forced speed of 50G:
dpdk-testpmd -c 0xff  -- -i  --eth-link-speed  50000

Signed-off-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>