[2209] Pass objects by const reference

Passing it as const RRClass (and making a copy) makes no real sense. It
looks more expected with the reference and might even be slightly
faster.

src/lib/datasrc/memory/memory_client.cc

@@ -221,7 +221,7 @@ private:
     bool separate_rrs_;
     bool ready_;
 public:
-    MemoryIterator(const RRClass rrclass,
+    MemoryIterator(const RRClass& rrclass,
                    const ZoneTree& tree, const Name& origin,
                    bool separate_rrs) :
         rrclass_(rrclass),

src/lib/datasrc/memory/zone_data_loader.cc

@@ -165,7 +165,7 @@ ZoneDataLoader::getCurrentName() const {
 
 ZoneData*
 loadZoneDataInternal(util::MemorySegment& mem_sgmt,
-                     const isc::dns::RRClass rrclass,
+                     const isc::dns::RRClass& rrclass,
                      const Name& zone_name,
                      boost::function<void(LoadCallback)> rrset_installer)
 {
@@ -223,7 +223,7 @@ generateRRsetFromIterator(ZoneIterator* iterator, LoadCallback callback) {
 
 ZoneData*
 loadZoneData(util::MemorySegment& mem_sgmt,
-             const isc::dns::RRClass rrclass,
+             const isc::dns::RRClass& rrclass,
              const isc::dns::Name& zone_name,
              const std::string& zone_file)
 {
@@ -236,7 +236,7 @@ loadZoneData(util::MemorySegment& mem_sgmt,
 
 ZoneData*
 loadZoneData(util::MemorySegment& mem_sgmt,
-             const isc::dns::RRClass rrclass,
+             const isc::dns::RRClass& rrclass,
              const isc::dns::Name& zone_name,
              ZoneIterator& iterator)
 {

src/lib/datasrc/memory/zone_data_loader.h

@@ -48,7 +48,7 @@ struct EmptyZone : public InvalidParameter {
 /// \param zone_name The name of the zone that is being loaded.
 /// \param zone_file Filename which contains the zone data for \c zone_name.
 ZoneData* loadZoneData(util::MemorySegment& mem_sgmt,
-                       const isc::dns::RRClass rrclass,
+                       const isc::dns::RRClass& rrclass,
                        const isc::dns::Name& zone_name,
                        const std::string& zone_file);
 
@@ -65,7 +65,7 @@ ZoneData* loadZoneData(util::MemorySegment& mem_sgmt,
 /// \param zone_name The name of the zone that is being loaded.
 /// \param iterator Iterator that returns RRsets to load into the zone.
 ZoneData* loadZoneData(util::MemorySegment& mem_sgmt,
-                       const isc::dns::RRClass rrclass,
+                       const isc::dns::RRClass& rrclass,
                        const isc::dns::Name& zone_name,
                        ZoneIterator& iterator);