OCMulticast start and stop APIs

OCMulticast start and stop APIs

APIs to start and stop multicast traffic. For stopping and staring multicast traffic
it manipulates multicast fd and IP_DROP_MEMBERSHIP.

OCStopMulticastTraffic interface is called from rd_client. It stops the multicast traffic.

OCStartMulticastTraffic is implemented but it is not called as this functionality is
not yet implemented.

Change-Id: If56c7af074cbba097b7b23d1abd787093872418a
Signed-off-by: Habib Virji <habib.virji@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/2387
Reviewed-by: Abhishek Sharma <ce.abhishek@samsung.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Abhishek Pandey <abhi.siso@samsung.com>
Reviewed-by: Patrick Lankswert <patrick.lankswert@intel.com>