Add the DTrace probe definitions for plockstat support.

This will be connected to the system later.

Sponsored by:	The FreeBSD Foundation
Correct format string to fix build of uhsoctl when DEBUG is defined

PR:		185007
Submitted by:	saper saper.info
MFC after:	3 days
Use %zu not %zd for printing size_t.

PR:		185007
Submitted by:	saper saper.info
MFC after:	3 days
bsd.dep.mk: add support for generating DTrace header files from .d files.

MFC after:	3 weeks
Check the number of returned entries before doing any access to ifm_ulist.
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.
Make REPORT TARGET PORT GROUPS to return something more sensible.

It requires more formalized LUN mapping to be exactly correct.
Add support for SCSI Ports VPD page.

Ports should also be filtered by LUN mapping.
Change ctl_add_initiator()/ctl_remove_initiator() KPI.

 - Store data in struct ctl_port to make it dynamic;
 - Make ctl_add_initiator() to choose free iid if caller passed < 0;
 - Remove unneeded now pool of iids from iSCSI.
Add support for READ FULL STATUS action of PERSISTENT RESERVE IN.

So far without initiator IDs.
Add initiator transport IDs to READ FULL STATUS.

This is a hack. Should be rewritten somehow to store full IDs, but still
not consume 512KB of RAM per target.