nvmf: Switch several ioctls to using nvlists

For requests that handoff queues from userspace to the kernel as well
as the request to fetch reconnect parameters from the kernel, switch
from using fla

nvmf: Switch several ioctls to using nvlists

For requests that handoff queues from userspace to the kernel as well
as the request to fetch reconnect parameters from the kernel, switch
from using flat structures to nvlists. In particular, this will
permit adding support for additional transports in the future without
breaking the ABI of the structures.

Note that this is an ABI break for the ioctls used by nvmf(4) and
nvmft(4). Since this is only present in main I did not bother
implementing compatability shims.

Inspired by: imp (suggestion on a different review)
Reviewed by: imp
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D48230

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nvmf: The in-kernel NVMe over Fabrics host

This is the client (initiator in SCSI terms) for NVMe over Fabrics.
Userland is responsible for creating a set of queue pairs and then
handing them off via

nvmf: The in-kernel NVMe over Fabrics host

This is the client (initiator in SCSI terms) for NVMe over Fabrics.
Userland is responsible for creating a set of queue pairs and then
handing them off via an ioctl to this driver, e.g. via the 'connect'
command from nvmecontrol(8). An nvmeX new-bus device is created
at the top-level to represent the remote controller similar to PCI
nvmeX devices for PCI-express controllers.

As with nvme(4), namespace devices named /dev/nvmeXnsY are created and
pass through commands can be submitted to either the namespace devices
or the controller device. For example, 'nvmecontrol identify nvmeX'
works for a remote Fabrics controller the same as for a PCI-express
controller.

nvmf exports remote namespaces via nda(4) devices using the new NVMF
CAM transport. nvmf does not support nvd(4), only nda(4).

Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D44714

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