net/linklayer: Implement loop back to own IP address

IP packets, sent to the own IP address, will be looped back
to the receiver.

Issue #488

lib/net/linklayer.cpp

@@ -132,6 +132,17 @@ boolean CLinkLayer::Send (const CIPAddress &rReceiver, const void *pIPPacket, un
 		return FALSE;
 	}
 
+	assert (pIPPacket != 0);
+	assert (nLength > 0);
+	assert (m_pNetConfig != 0);
+	if (   !rReceiver.IsNull ()
+	    && rReceiver == *m_pNetConfig->GetIPAddress ())
+	{
+		m_IPRxQueue.Enqueue (pIPPacket, nLength);	// loop back to own address
+
+		return TRUE;
+	}
+
 	u8 FrameBuffer[nFrameLength];
 	TEthernetHeader *pHeader = (TEthernetHeader *) FrameBuffer;
 
@@ -142,11 +153,8 @@ boolean CLinkLayer::Send (const CIPAddress &rReceiver, const void *pIPPacket, un
 
 	pHeader->nProtocolType = BE (ETH_PROT_IP);
 
-	assert (pIPPacket != 0);
-	assert (nLength > 0);
 	memcpy (FrameBuffer+sizeof (TEthernetHeader), pIPPacket, nLength);
 
-	assert (m_pNetConfig != 0);
 	assert (m_pARPHandler != 0);
 	CMACAddress MACAddressReceiver;
 	if (   rReceiver.IsBroadcast ()