routing: use amount to send for time lock weight

The time lock weight for a hop is supposed to be proportional to the
amount that is sent/locked, but in a previous change we switched to the
net amount, where inbound fees aren't yet applied. This is corrected in
this commit.

routing/pathfind.go

@@ -823,7 +823,7 @@ func findPath(g *graphParams, r *RestrictParams, cfg *PathFindingConfig,
 		// weight composed of the fee that this node will charge and
 		// the amount that will be locked for timeLockDelta blocks in
 		// the HTLC that is handed out to fromVertex.
-		weight := edgeWeight(netAmountToReceive, fee, timeLockDelta)
+		weight := edgeWeight(amountToSend, fee, timeLockDelta)
 
 		// Compute the tentative weight to this new channel/edge
 		// which is the weight from our toNode to the target node