When setting vlan, hns3 driver will add vlan entry to vlan linked list
each time, and this is unreasonable.
This patch adds a check whether the VLAN to be added already exists
in the linked list and prevents adding duplicated vlan.
Fixes: 411d23b9eafb ("net/hns3: support VLAN")
Cc: stable@dpdk.org
Signed-off-by: Min Hu (Connor) <humin29@huawei.com>
Signed-off-by: Wei Hu (Xavier) <xavier.huwei@huawei.com>