RDMA/ionic: Embed counter driver data in rdma_counter allocation

In the Linux kernel, the following vulnerability has been resolved: RDMA/ionic: Embed counter driver data in rdma_counter allocation Commit 7e53b31acc7f ("RDMA/core: Create and destroy rdma_counter using rdma_zalloc_drv_obj()") requires drivers implementing counter ops to embed struct rdma_counter in a driver-specific struct, register its size via INIT_RDMA_OBJ_SIZE, and provide a counter_init callback. The ionic driver was merged without this adaptation, causing a NULL pointer dereference in alloc_and_bind() since rdma_zalloc_drv_obj() allocates zero bytes when size_rdma_counter is unset. Consolidate struct ionic_counter into a new struct ionic_rdma_counter that embeds struct rdma_counter, replace the xarray with a lightweight ida for ID allocation, and add the required counter_init and INIT_RDMA_OBJ_SIZE declarations.