[2726] Pass params by reference

This is mostly to silence cppcheck, than to save some CPU power (with
int it makes little sense) and it is less noisy than to put suppression
there.

src/lib/statistics/counter.h

@@ -55,7 +55,7 @@ public:
     /// \param type %Counter item to increment
     ///
     /// \throw isc::OutOfRange \a type is invalid
-    void inc(const Counter::Type type) {
+    void inc(const Counter::Type& type) {
         if (type >= counters_.size()) {
             isc_throw(isc::OutOfRange, "Counter type is out of range");
         }
@@ -68,7 +68,7 @@ public:
     /// \param type %Counter item to get the value of
     ///
     /// \throw isc::OutOfRange \a type is invalid
-    const Counter::Value& get(const Counter::Type type) const {
+    const Counter::Value& get(const Counter::Type& type) const {
         if (type >= counters_.size()) {
             isc_throw(isc::OutOfRange, "Counter type is out of range");
         }