dcb.b:dcb_final_free:replaced ((dcb->flags & DCBF_CLONE)==0) with macro !DCB_IS_CLONE(dcb)

readwritesplit.h:Removed invalid macros which assumed that ROUTER_CLIENT_SES->rses_backend_ref always pointed to valid and used backend reference and thus included potential risk of NULL-pointer refernce.
mysql_backend.c and mysql_client.c:avoid executing CHK_PROTOCOL(p) after original DCB has been released the memory.
readwritesplit.c:Replaced RSES_CLEINT_DCB macro with a function which returns client DCB for a given router client session.

server/modules/include/readwritesplit.h

@@ -323,8 +323,5 @@ typedef struct router_instance {
 #define BACKEND_TYPE(b) (SERVER_IS_MASTER((b)->backend_server) ? BE_MASTER :    \
         (SERVER_IS_SLAVE((b)->backend_server) ? BE_SLAVE :  BE_UNDEFINED));
 
-#define RSES_SESSION(r) (r->rses_backend_ref->bref_dcb->session)  
-
-#define RSES_CLIENT_DCB(r) (RSES_SESSION(r)->client)
-     
+    
 #endif /*< _RWSPLITROUTER_H */