Add CTL support for REPORT IDENTIFYING INFORMATION command.

It allows to report to initiator LU identifying information, preset via
"ident_info" and "text_ident_info" options.

Unfortunately it is impossible to implement SET IDENTIFYING INFORMATION,
since we have no persistent storage it requires, so the information is
read-only for initiator and has to be set out-of-band.

MFC after: 1 week
Sponsored by: iXsystems, Inc.