nvme-fabrics: check ioccsz and iorcsz

Make sure that ioccsz and iorcsz returned by target are correct before use it.

Per 2.0a base NVMe spec:

  I/O Queue Command Capsule Supported Size (IOCCSZ): This field defines
  the maximum I/O command capsule size in 16 byte units. The minimum value
  that shall be indicated is 4 corresponding to 64 bytes.

Signed-off-by: Guixin Liu <kanie@linux.alibaba.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>