Move SetLayerSet to const reference

Avoids potential performance inefficiencies

include/board_item.h

@@ -250,7 +250,7 @@ public:
             return LSET( m_layer );
     }
 
-    virtual void SetLayerSet( LSET aLayers )
+    virtual void SetLayerSet( const LSET& aLayers )
     {
         if( aLayers.count() == 1 )
         {

pcbnew/pad.h

@@ -384,7 +384,7 @@ public:
         m_polyDirty[ERROR_OUTSIDE] = true;
     }
 
-    void SetLayerSet( LSET aLayers ) override   { m_padStack.SetLayerSet( aLayers ); }
+    void SetLayerSet( const LSET& aLayers ) override   { m_padStack.SetLayerSet( aLayers ); }
     LSET GetLayerSet() const override           { return m_padStack.LayerSet(); }
 
     void SetAttribute( PAD_ATTRIB aAttribute );

pcbnew/pcb_track.cpp

@@ -917,7 +917,7 @@ LSET PCB_VIA::GetLayerSet() const
 }
 
 
-void PCB_VIA::SetLayerSet( LSET aLayerSet )
+void PCB_VIA::SetLayerSet( const LSET& aLayerSet )
 {
     bool first = true;
 

pcbnew/pcb_track.h

@@ -418,7 +418,7 @@ public:
      * Note SetLayerSet() initialize the first and last copper layers connected by the via.
      * So currently SetLayerSet ignore non copper layers
      */
-    virtual void SetLayerSet( LSET aLayers ) override;
+    virtual void SetLayerSet( const LSET& aLayers ) override;
 
     /**
      * For a via m_layer contains the top layer, the other layer is in m_bottomLayer/

pcbnew/zone.cpp

@@ -282,7 +282,7 @@ void ZONE::SetLayer( PCB_LAYER_ID aLayer )
 }
 
 
-void ZONE::SetLayerSet( LSET aLayerSet )
+void ZONE::SetLayerSet( const LSET& aLayerSet )
 {
     if( aLayerSet.count() == 0 )
         return;

pcbnew/zone.h

@@ -126,7 +126,7 @@ public:
     void GetMsgPanelInfo( EDA_DRAW_FRAME* aFrame, std::vector<MSG_PANEL_ITEM>& aList ) override;
     wxString GetFriendlyName() const override;
 
-    void SetLayerSet( LSET aLayerSet ) override;
+    void SetLayerSet( const LSET& aLayerSet ) override;
     virtual LSET GetLayerSet() const override { return m_layerSet; }
 
     const wxString& GetZoneName() const { return m_zoneName; }