MFC r268287:
Implement and use ctl_frontend_find().
MFC r268288:
Improve CTL_BEARG_* flags support, including optional values copyout.
MFC r268291:
Create separate CTL port for every iSCSI target (and maybe portal group).

Having single port for all iSCSI connections makes problematic implementing
some more advanced SCSI functionality in CTL, that require proper ports
enumeration and identification.

This change extends CTL iSCSI API, making ctld daemon to control list of
iSCSI ports in CTL.  When new target is defined in config fine, ctld will
create respective port in CTL.  When target is removed -- port will be
also removed after all active commands through that port properly aborted.
This change require ctld to be rebuilt to match the kernel.

As a minor side effect, this allows to have iSCSI targets without LUNs.
While that may look odd and not very useful, that is not incorrect.
MFC r268293:
Burry devid port method, which was a gross hack.

Instead make ports provide wanted port and target IDs, and LUNs provide
wanted LUN IDs.  After that core Device ID VPD code only had to link all
of them together and add relative port and port group numbers.

LUN ID for iSCSI LUNs no longer created by CTL, but by ctld, and passed
to CTL as "scsiname" LUN option.  This makes LUNs to report the same set
of IDs, independently from the port through which it is accessed, as
required by SCSI specifications.
MFC r268302:
Pass through iSCSI session ISID from LOGIN request to the CTL frontend.

ISID is an important part of initiator transport ID for iSCSI.  It is not
used now, but should be to properly implement persistent reservation.
MFC r268307:
Move lun_map() method from command nexus to port.

Previous implementation made impossible to do some things, such as calling
it for ports other then one through which command arrived.
MFC r268308:
Make REPORT TARGET PORT GROUPS command report realistic data instead of
hardcoded garbage.
MFC r268309:
Add support for SCSI Ports (88h) VPD page.
MFC r268328:
Close race in r268291 between port destruction, delayed by sessions
teardown, and new port creation during `service ctld restart`.

Close it by returning iSCSI port internal state, that allows to identify
dying ports, which should not be counted as existing, from really alive.
MFC r268330:
Make gcc happy, init idlen2.
MFC r268353:
Implement ABORT TASK SET and I_T NEXUS RESET task management functions.

Use the last one to terminate active commands on iSCSI session termination.
Previous code was aborting only commands doing some data moves.
MFC r268356, r268357:
When new connection comes in, check whether we already have session from
the same intiator (Name+ISID).  If so -- terminate the old session and let
the new one take its place, as required by iSCSI RFC.
MFC r268362:
Teach ctl_add_initiator() to dynamically allocate IIDs from pool.

If port passed negative IID value, the function will try to allocate IID
from the pool of unused, based on passed wwpn or name arguments.  It does
all its best to make IID unique and persistent across reconnects.

This makes persistent reservation properly work for iSCSI.  Previously,
in case of reconnects, reservation could be unexpectedly lost, or even
migrate between intiators.
MFC r268363:
Add support for READ FULL STATUS action of PERSISTENT RESERVE IN command.
MFC r268364:
Fix "use after free" on port creation error in r268291.
MFC r268387:
Fix task management functions status: task not found is not an error,
while not implemented function is.
MFC r268418:
Enable TAS feature: notify initiator if its command was aborted by other.

That should make operation more kind to multi-initiator environment.
Without this, other initiators may find out that something bad happened
to their commands only via command timeout.
MFC r268421:
Remove status setting from datamove() path.  Leave that to other places.
MFC r268447:
Add LUN options to specify 64-bit EUI and NAA identifiers.
MFC r268240 (by ken):
Add persistent reservation support to camcontrol(8).

camcontrol(8) now supports a new 'persist' subcommand that allows users to
issue SCSI PERSISTENT RESERVE IN / OUT commands.