For MLO, we need to designate one of the link vdev
as mlo vdev, on which FW will accept the multicast
frames and for the other link will drop the mcast frames.
So as part of vdev start, we indicate the mlo mcast
vdev in the first vdev of the mlo.
Change-Id: Ic962a6e1fead4a3cab7c622583392ecf373f4783
CRs-Fixed: 3080525