Rework CTL frontend & backend options to use nv(3), allow creating multiple
ioctl frontend ports.

This revision introduces two changes to CTL:

• Changes the way options are passed to CTL_LUN_REQ and CTL_PORT_REQ ioctls. Removes ctl_be_arg structure and associated logic and replaces it with nv(3)-based logic for passing in and out arguments.
• Allows creating multiple ioctl frontend ports using either ctladm(8) or ctld(8). New frontend ports are represented by /dev/cam/ctl<pp>.<vp> nodes, eg /dev/cam/ctl5.3. Those device nodes respond only to CTL_IO ioctl.

New command-line options for ctladm:

creates new ioctl frontend port with using free pp and vp=0

ctladm port -c

creates new ioctl frontend port with pp=10 and vp=0

ctladm port -c -O pp=10

creates new ioctl frontend port with pp=11 and vp=12

ctladm port -c -O pp=11 -O vp=12

removes port with number 4 (it's a "targ_port" number, not pp number)

ctladm port -r -p 4

New syntax for ctl.conf:
target ... {

port ioctl/<pp>
...

}

target ... {

port ioctl/<pp>/<vp>
...

Note: Most of this work was made by jceel@, thank you.

Submitted by: jceel
Reworked by: myself
Reviewed by: mav (earlier versions and recently during the rework)
Obtained from: FreeNAS and TrueOS
Relnotes: Yes
Sponsored by: iXsystems Inc.
Differential Revision: https://reviews.freebsd.org/D9299