netdev-dpdk: Support the link speed of XL710

netdev-dpdk: Support the link speed of XL710

In the scenario of XL710, the link speed which stored in the table
of Interface is not 40G. Because the implementation of query of link
speed only support to 10G, the parameter 'current' will be a random
value in the scenario of higher link speed. In this case, incorrect
link speed of XL710 nic will be stored in the database.

Signed-off-by: Xu Binbin <xu.binbin1@zte.com.cn>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>