transport, redis: Move total_connections to generic_server::server class

Both cql_server and redis_server have the same "total_connections"
member variable so pull that up to the generic_server::server base
class.

generic_server.hh

@@ -46,6 +46,7 @@ protected:
     promise<> _all_connections_stopped;
     uint64_t _current_connections = 0;
     uint64_t _connections_being_accepted = 0;
+    uint64_t _total_connections = 0;
 
 public:
     virtual ~server();

redis/server.cc

@@ -154,7 +154,7 @@ redis_server::connection::connection(redis_server& server, socket_address server
     , _write_buf(_fd.output())
     , _options(server._config._read_consistency_level, server._config._write_consistency_level, server._config._timeout_config, server._auth_service, addr, server._total_redis_db_count)
 {
-    ++_server._stats._total_connections;
+    ++_server._total_connections;
     ++_server._current_connections;
     _server._connections_list.push_back(*this);
 }

redis/stats.hh

@@ -50,7 +50,6 @@ public:
     uint64_t _connections = 0;
     uint64_t _requests_served = 0;
     uint64_t _requests_serving = 0;
-    uint64_t _total_connections = 0;
     utils::estimated_histogram _estimated_requests_latency;
     utils::timed_rate_moving_average_and_histogram _requests;
 private:

transport/server.hh

@@ -272,7 +272,6 @@ private:
 private:
     future<> _stopped = _all_connections_stopped.get_future();
     boost::intrusive::list<connection> _connections_list;
-    uint64_t _total_connections = 0;
 private:
     future<> advertise_new_connection(shared_ptr<connection> conn);
     future<> unadvertise_connection(shared_ptr<connection> conn);