[IOT-2874] Do not drop CON duplicated requests

According to COAP spec section 4.5, confirmable duplicated 
requests should not be silently dropped, instead they need 
to be acknowledged every time. Therefore check if message 
is confirmable before dropping it.

Change-Id: Ie7a49da9f7869fc11f679054fe8dd5c78684eb53
Signed-off-by: Veeraj Khokale <veeraj.sk@samsung.com>

resource/csdk/connectivity/src/camessagehandler.c

@@ -202,7 +202,8 @@ static CAData_t* CAGenerateHandlerData(const CAEndpoint_t *endpoint,
             goto exit;
         }
 
-        if (CADropSecondMessage(&caglobals.ca.requestHistory, endpoint, reqInfo->info.messageId,
+        if ((reqInfo->info.type != CA_MSG_CONFIRM) &&
+            CADropSecondMessage(&caglobals.ca.requestHistory, endpoint, reqInfo->info.messageId,
                                 reqInfo->info.token, reqInfo->info.tokenLength))
         {
             OIC_LOG(INFO, TAG, "Second Request with same Token, Drop it");