We were always ordering heap by distance, not score (which are different
if we are routing by cheapest, not shortest!).
This simplifies our callbacks, too.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
The user supplies callbacks to do channel selection and comparison.
Note that this continues to map the entire network; not just to the
source, for use with random routing.
Benchmarks: (using current mainnet gossip store)
/devtools/route gossip-store-2020-07-27 all 03c981ed4ad15837f29a212dc8cf4b31f274105b7c95274a41449bf496ebd2fe10 | grep 'Time to find path'
With nothing (i.e. DEVELOPER build)
Averages 17ms
With -Og (i.e. standard non-DEVELOPER build)
Averages 14ms
With -O3 -flto:
Averages 4ms
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
