[2317] Eliminated cppcheck errors.

src/bin/dhcp4/config_parser.cc

@@ -1118,7 +1118,7 @@ private:
         // Check the option definition parameters are valid.
         try {
             def->validate();
-        } catch (const isc::Exception ex) {
+        } catch (const isc::Exception& ex) {
             isc_throw(DhcpConfigError, "invalid option definition"
                       << " parameters: " << ex.what());
         }

src/bin/dhcp6/config_parser.cc

@@ -1148,7 +1148,7 @@ private:
         // Check the option definition parameters are valid.
         try {
             def->validate();
-        } catch (const isc::Exception ex) {
+        } catch (const isc::Exception& ex) {
             isc_throw(DhcpConfigError, "invalid option definition"
                       << " parameters: " << ex.what());
         }

src/bin/dhcp6/dhcp6_srv.cc

@@ -404,7 +404,7 @@ void Dhcpv6Srv::sanityCheck(const Pkt6Ptr& pkt, RequirementLevel clientid,
     Option::OptionCollection server_ids = pkt->getOptions(D6O_SERVERID);
     switch (serverid) {
     case FORBIDDEN:
-        if (server_ids.size() > 0) {
+        if (!server_ids.empty()) {
             isc_throw(RFCViolation, "Exactly 1 server-id option expected, but "
                       << server_ids.size() << " received in " << pkt->getName());
         }

src/bin/dhcp6/tests/config_parser_unittest.cc

@@ -81,7 +81,7 @@ public:
             params["code"] = "38";
             params["data"] = "AB CDEF0105";
             params["csv-format"] = "False";
-        } else if (parameter == "name") {
+        } else if (parameter == "space") {
             params["name"] = "subscriber-id";
             params["space"] = param_value;
             params["code"] = "38";