Move C++ code out of C headers

The additions into the server.h header used C++ language which caused C
programs to fail to compile. Moved the implementation of the EMAverage
class into the private Server class in the server.hh header and exposed it
via functions in the server.h header. Also temporarily moved
almost_equal_server_scores into the public server.hh as there is no
service.hh header.

include/maxscale/server.h

@@ -20,7 +20,6 @@
 
 #include <maxscale/cdefs.h>
 #include <maxbase/jansson.h>
-#include <maxbase/average.hh>
 #include <maxscale/config.h>
 #include <maxscale/dcb.h>
 
@@ -166,9 +165,6 @@ typedef struct server
                                                  *   by rwsplit. TODO: Move to rwsplit */
     bool                   warn_ssl_not_enabled;/**< SSL not used for an SSL enabled server */
     MxsDiskSpaceThreshold* disk_space_threshold;/**< Disk space thresholds */
-    // TODO, this is a plain ptr to a C++ class. Soonish, when the server is new/deleted
-    // this will become a std::unique ptr. But not in this commit.
-    maxbase::EMAverage* response_time;      /**< for calculating average response time */
 } SERVER;
 
 /**
@@ -528,4 +524,7 @@ extern void dprintServer(DCB*, const SERVER*);
 extern void dprintPersistentDCBs(DCB*, const SERVER*);
 extern void dListServers(DCB*);
 
+int server_response_time_num_samples(const SERVER* server);
+double server_response_time_average(const SERVER* server);
+
 MXS_END_DECLS