net: hns3: only enable unicast promisc when mac table full

Currently, the driver will enable unicast promisc for the function
once configure mac address fail. It's unreasonable when the failure
is caused by using same mac address with other functions. So only
enable unicast promisc when mac table full.

Fixes: c631c696 ("net: hns3: refactor the promisc mode setting")
Signed-off-by: Jian Shen <shenjian15@huawei.com>
Signed-off-by: Jijie Shao <shaojijie@huawei.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>