Add discovery-filter.  This makes it possible to restrict which targets
are returned during discovery based on initiator portal, name, and CHAP
credentials.

Reviewed by:	mav@
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273813 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Simplify code; no functional changes.

MFC after:	1 month
Sponsored by:	The FreeBSD Foundation


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273816 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f