Consider max_htlc when determining effective capacity of route hint channels

Testing is added in the next commit.

Author: valentinewallace

lightning/src/routing/router.rs

@@ -946,7 +946,10 @@ impl<'a> CandidateRouteHop<'a> {
 				liquidity_msat: details.next_outbound_htlc_limit_msat,
 			},
 			CandidateRouteHop::PublicHop { info, .. } => info.effective_capacity(),
-			CandidateRouteHop::PrivateHop { .. } => EffectiveCapacity::Infinite,
+			CandidateRouteHop::PrivateHop { hint } => {
+				hint.htlc_maximum_msat.map_or(EffectiveCapacity::Infinite,
+					|amt| EffectiveCapacity::MaximumHTLC { amount_msat: amt })
+			}
 		}
 	}
 }