nvme-fabrics: check more command sizes

struct common_command provides a common structure for NVMe-oF command
format.  It also needs to be checked for unintended size growth.

Signed-off-by: Minwoo Im <minwoo.im.dev@gmail.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>