nvmet: reorder fields in 'struct nvmf_ctrl_options'

Group some variables based on their sizes to reduce holes.
On x86_64, this shrinks the size of 'struct nvmf_ctrl_options' from 136 to
128 bytes.

When such a structure is allocated in nvmf_create_ctrl(), because of the
way memory allocation works, when 136 bytes were requested, 192 bytes were
allocated.

So this saves 64 bytes per allocation, 1 cache line to hold the whole
structure and a few cycles when zeroing the memory in nvmf_create_ctrl().

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>