Ratsnest default value for tracks and vias

Fixes: lp:1851611
* https://bugs.launchpad.net/kicad/+bug/1851611

(cherry picked from commit 6182133a4e)
(slightly modified due to differences between master and 5.1)

pcbnew/router/pns_kicad_iface.cpp

@@ -1255,6 +1255,7 @@ void PNS_KICAD_IFACE::AddItem( PNS::ITEM* aItem )
 
     if( newBI )
     {
+        newBI->SetLocalRatsnestVisible( m_board->IsElementVisible( LAYER_RATSNEST ) );
         aItem->SetParent( newBI );
         newBI->ClearFlags();