The NVMe emulation checked if the Asynchronous Event Request Limit
(a.k.a AERL) would be exceeded in pci_nvme_aer_add(), but this function
is only called from nvme_opc_async_event_req() which also checks for
exceeding the AERL.
While in the neighborhood, fix / enhance the debug logging.
Tested by:
MFC after: 2 weeks