app/testpmd: fix VLAN configuration on failure

app/testpmd: fix VLAN configuration on failure

When failing to configure VLAN offloads after the port was started, there
is no need to update the port configuration. Currently, when user
configure an unsupported VLAN offloads and fails, and then restart the
port, it will fails since the configuration has been refreshed.

This patch makes the function return directly instead of refreshing the
configuration when execution fails.

Fixes: 384161e00627 ("app/testpmd: adjust on the fly VLAN configuration")
Cc: stable@dpdk.org
Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>
Signed-off-by: Wei Hu (Xavier) <xavier.huwei@huawei.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>