MXS-2027: Store LOAD DATA state inside MXS_SESSION

By storing the data gathere by readwritesplit inside the session, the
protocol will be aware of the state of the LOAD DATA LOCAL INFILE
execution. This prevents misinterpretation of the data which previously
led to closed connections, effectively rendering LOAD DATA LOCAL INFILE
unusable.

This change is a temporary solution to a problem that needs to be solved
at the protocol level. The changes required to implement this are too big
to add into a bug fix release.

server/core/session.cc

@@ -130,6 +130,7 @@ static MXS_SESSION* session_alloc_body(SERVICE* service, DCB* client_dcb,
     session->stmt.target = NULL;
     session->qualifies_for_pooling = false;
     session->close_reason = SESSION_CLOSE_NONE;
+    session->load_active = false;
 
     MXS_CONFIG *config = config_get_global_options();
     // If MaxScale is running in Oracle mode, then autocommit needs to