net/hns3: fix reporting undefined speed

net/hns3: fix reporting undefined speed

There may be a case in future that the speed obtained from firmware
is undefined (such as, 400G or other rate), and link status of device is
up. At this case, PMD driver will reports 100Mbps to the user in the
"hns3_dev_link_update" API, which is unreasonable. Besides, if the
speed from firmware is zero, driver should report zero instead of
100Mbps.

Fixes: 59fad0f32135 ("net/hns3: support link update operation")
Cc: stable@dpdk.org
Signed-off-by: Huisong Li <lihuisong@huawei.com>
Signed-off-by: Min Hu (Connor) <humin29@huawei.com>