nvmf: Align members of spdk_nvmf_subsystem

Signed-off-by: Ben Walker <benjamin.walker@intel.com>
Change-Id: Iad0ea4418ffa2cb6a951b06d7f413df988ba640f
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/4552


Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Community-CI: Broadcom CI
Community-CI: Mellanox Build Bot
Reviewed-by: Aleksey Marchuk <alexeymar@mellanox.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>