Fix multicast from Ncp Host going back to host (#1910)

* fix multicast from Ncp Host going back to host

* rename SendFromNcpHost to SendRaw

src/core/api/ip6_api.cpp

@@ -162,8 +162,8 @@ otError otIp6Send(otInstance *aInstance, otMessage *aMessage)
 
     otLogFuncEntry();
 
-    error = aInstance->mIp6.HandleDatagram(*static_cast<Message *>(aMessage), NULL,
-                                           aInstance->mThreadNetif.GetInterfaceId(), NULL, true);
+    error = aInstance->mIp6.SendRaw(*static_cast<Message *>(aMessage),
+                                    aInstance->mThreadNetif.GetInterfaceId());
 
     otLogFuncExitErr(error);
 

src/core/net/ip6.cpp

@@ -654,6 +654,32 @@ exit:
     return error;
 }
 
+otError Ip6::SendRaw(Message &aMessage, int8_t aInterfaceId)
+{
+    otError error = OT_ERROR_NONE;
+    Header header;
+    MessageInfo messageInfo;
+
+    // check aMessage length
+    VerifyOrExit(aMessage.Read(0, sizeof(header), &header) == sizeof(header), error = OT_ERROR_DROP);
+
+    messageInfo.SetPeerAddr(header.GetSource());
+    messageInfo.SetSockAddr(header.GetDestination());
+    messageInfo.SetInterfaceId(aInterfaceId);
+    messageInfo.SetHopLimit(header.GetHopLimit());
+    messageInfo.SetLinkInfo(NULL);
+
+    if (header.GetDestination().IsMulticast())
+    {
+        SuccessOrExit(error = InsertMplOption(aMessage, header, messageInfo));
+    }
+
+    error = HandleDatagram(aMessage, NULL, aInterfaceId, NULL, true);
+
+exit:
+    return error;
+}
+
 otError Ip6::HandleDatagram(Message &aMessage, Netif *aNetif, int8_t aInterfaceId, const void *aLinkMessageInfo,
                             bool aFromNcpHost)
 {
@@ -711,11 +737,6 @@ otError Ip6::HandleDatagram(Message &aMessage, Netif *aNetif, int8_t aInterfaceI
         else
         {
             forward = true;
-
-            if (aFromNcpHost)
-            {
-                SuccessOrExit(error = InsertMplOption(aMessage, header, messageInfo));
-            }
         }
     }
     else

src/core/net/ip6.hpp

@@ -132,6 +132,18 @@ public:
      */
     otError SendDatagram(Message &aMessage, MessageInfo &aMessageInfo, IpProto aIpProto);
 
+    /**
+     * This method sends a raw IPv6 datagram with a fully formed IPv6 header.
+     *
+     * @param[in]  aMessage          A reference to the message.
+     * @param[in]  aInterfaceId      The interface identifier of the network interface that received the message.
+     *
+     * @retval OT_ERROR_NONE   Successfully processed the message.
+     * @retval OT_ERROR_DROP   Message processing failed and the message should be dropped.
+     *
+     */
+    otError SendRaw(Message &aMessage, int8_t aInterfaceId);
+
     /**
      * This method processes a received IPv6 datagram.
      *