port/linux/ipadapter: fix multicast config
port/linux/ipadapter: fix multicast config

* Set scope_id into outgoing message for each
  interface in oc_send_discovery_request().
* Iterate through all interfaces to add IPv6
  multicast membership inside
  add_mcast_sock_to_ipv6_multicast_group().

Change-Id: Ie0d754fe20e8c7b0faee69e83f0878cc4ed9529a
Signed-off-by: Kishen Maloor <c62ddea3cd661a9268bff15f07fc2229cdc9ac02@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/23769

iotivity/iotivity-constrained,iotivity/iotivity-constrained,iotivity/iotivity-constrained,iotivity/iotivity-constrained