Fixed vnic issue after saturn reset

Fixed vnic issue after saturn reset

After saturn reboots uVnic will not recover
The issue happens When a host connected to NM3 via infiniband switch.
The fact here is xve driver sets OPER_DOWN when it losses HEART_BEAT and
there is no way for it set this state back .
Fixing this by disjoining Multicast group once HeartBeat is lost and
joining back once saturn comes back

Orabug: 22862488

Reported-by: Ye Jin <ye.jin@oracle.com>
Signed-off-by: Pradeep Gopanapalli <pradeep.gopanapalli@oracle.com>
Reviewed-by: sajid zia <szia@oracle.com>
Signed-off-by: Qing Huang <qing.huang@oracle.com>