mlx4_vnic: use the mlid while calling ib_detach_mcast

mlx4_vnic: use the mlid while calling ib_detach_mcast

In mlx4_vnic, vnic_mcast_detach_ll() calls ib_detach_mcast() with the port lid
instead of the mlid resulting in multicast detach to fail. This caused
the subsequent multicast attach to fail.

Orabug: 29029705

Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
Acked-by:    John Haxby <john.haxby@oracle.com>
Reviewed-by: Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com>
Reviewed-by: Håkon Bugge <haakon.bugge@oracle.com>
Signed-off-by: aru kolappan <aru.kolappan@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>