vdpa: support set mac address from vdpa tool

vdpa: support set mac address from vdpa tool

Add new UAPI to support the mac address from vdpa tool
Function vdpa_nl_cmd_dev_attr_set_doit() will get the
new MAC address from the vdpa tool and then set it to the device.

The usage is: vdpa dev set name vdpa_name mac **:**:**:**:**:**

Here is example:
root@L1# vdpa -jp dev config show vdpa0
{
    "config": {
        "vdpa0": {
            "mac": "82:4d:e9:5d:d7:e6",
            "link ": "up",
            "link_announce ": false,
            "mtu": 1500
        }
    }
}

root@L1# vdpa dev set name vdpa0 mac 00:11:22:33:44:55

root@L1# vdpa -jp dev config show vdpa0
{
    "config": {
        "vdpa0": {
            "mac": "00:11:22:33:44:55",
            "link ": "up",
            "link_announce ": false,
            "mtu": 1500
        }
    }
}

Signed-off-by: Cindy Lu <lulu@redhat.com>
Message-Id: <20240731031653.1047692-2-lulu@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>