This is particularly interesting because we handle overflow during route
calculation now; this could happen in theory once we wumbo.
It fixes a thinko when we print out routehints, too: we want to print
them out literally, not print out the effect they have on fees (which
is in the route, which we also print).
This ABI change doesn't need a CHANGELOG, since paystatus is new since
release.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>