We don't set received_via for http because axum/hyper make it a
bit weird to access that information and it will require some
effort to figure out how to get that without breaking the
existing proxy-aware client IP determination.
This is implemented by allowing the Message:set_due method to
load the message metadata to consult the scheduling constraints,
which should mean that all scheduling updates have the constraints
applied to them.
M.L. Oelering
Tom Mairs
Wez Furlong