JORTE: fix bug in subscriber callback

This fixes a rarely occurring bug in subscriber callback.

When a Java subscriber is being destroyed, during the process
a JORTECallbackContext_t structure, used for storing pointers to Java objects,
was free()'d. If this occurred when new issue had arrived and was being
processed by the receive thread, then the pointer to the, now non-existent,
callback structure would have been dereferenced, leading to a SEGFAULT.

To fix this we now create a pointer to pointer to the specific structure
and pass this pointer to ORTESubcriptionCreate() and use it from the recvCallBack().