Update hsv3 spec for unreachable/failed single onion retries using 3 hops
This ticket is the spec part of legacy/trac#23818 (moved), legacy/trac#23507 (moved), and legacy/trac#23588 (moved).
This ticket is the spec part of legacy/trac#23818 (moved), legacy/trac#23507 (moved), and legacy/trac#23588 (moved).