routing: return *unifiedPolicyEdge in getPolicy

We encapsulate the capacity inside a unifiedPolicyEdge for later usage.
The meaning of "policy" has changed now, which will be refactored in the
next commmit.

routing/router.go

@@ -2837,10 +2837,11 @@ func (r *ChannelRouter) BuildRoute(amt *lnwire.MilliSatoshi,
 
 		// Add fee for this hop.
 		if !localChan {
-			runningAmt += policy.ComputeFee(runningAmt)
+			runningAmt += policy.policy.ComputeFee(runningAmt)
 		}
 
-		log.Tracef("Select channel %v at position %v", policy.ChannelID, i)
+		log.Tracef("Select channel %v at position %v",
+			policy.policy.ChannelID, i)
 
 		edges[i] = unifiedPolicy
 	}
@@ -2862,12 +2863,12 @@ func (r *ChannelRouter) BuildRoute(amt *lnwire.MilliSatoshi,
 
 		if i > 0 {
 			// Decrease the amount to send while going forward.
-			receiverAmt -= policy.ComputeFeeFromIncoming(
+			receiverAmt -= policy.policy.ComputeFeeFromIncoming(
 				receiverAmt,
 			)
 		}
 
-		pathEdges = append(pathEdges, policy)
+		pathEdges = append(pathEdges, policy.policy)
 	}
 
 	// Build and return the final route.