don't drop captured packets from remote MAC

We see such packets when a MAC that we previously saw at a remote peer
has been moved to ours. Dropping these packets cuts off network
connectivity for the new owner of the MAC.

Instead we update the MAC cache and flush the flows, to remove the now
incorrect entries for that MAC. And carry on as normal.

router/network_router.go

@@ -84,16 +84,15 @@ func (router *NetworkRouter) handleCapturedPacket(key PacketKey) FlowOp {
 	srcMac := net.HardwareAddr(key.SrcMAC[:])
 	dstMac := net.HardwareAddr(key.DstMAC[:])
 
-	switch newSrcMac, conflictPeer := router.Macs.Add(srcMac, router.Ourself.Peer); {
+	switch newSrcMac, conflictPeer := router.Macs.AddForced(srcMac, router.Ourself.Peer); {
 	case newSrcMac:
-		log.Println("Discovered local MAC", srcMac)
+		log.Print("Discovered local MAC ", srcMac)
 	case conflictPeer != nil:
-		// The MAC cache has an entry for the source MAC
-		// associated with another peer.  This probably means
-		// we are seeing a frame we injected ourself.  That
-		// shouldn't happen, but discard it just in case.
-		log.Error("Captured frame from MAC (", srcMac, ") to (", dstMac, ") associated with another peer ", conflictPeer)
-		return DiscardingFlowOp{}
+		// The MAC cache has an entry for the source MAC associated
+		// with another peer. This can happen when a MAC has moved.
+		log.Print("Discovered local MAC ", srcMac, " (was at ", conflictPeer, ")")
+		// We need to clear out any flows with the MAC as the source.
+		router.Overlay.(NetworkOverlay).InvalidateRoutes()
 	}
 
 	// Discard STP broadcasts