ctl: Add NVMF port type and ioctls

• Add CTL_PORT_NVMF as a new port type.

• Define a new CTL_NVMF ioctl for NVMF-specific operations similar to CTL_ISCSI. This ioctl supports a command to handoff a single queue pair, a command to enumerate active associations, and a command to disconnect one or more active associations.

Reviewed by: imp
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D44724