multi: break ChannelConstraints into two sub-structures

This commit breaks the ChannelConstraints structure into two
sub-structures that reflect the fundamental differences in how
these parameters are used. On its face it may not seem necessary,
however the distinction introduced here is relevant for how we
will be implementing the Dynamic Commitments proposal.

routing/localchans/manager.go

@@ -279,7 +279,7 @@ func (r *Manager) getHtlcAmtLimits(tx kvdb.RTx, chanPoint wire.OutPoint) (
 	// capacity AND less than or equal to the max in-flight HTLC value.
 	// Since the latter is always less than or equal to the former, just
 	// return the max in-flight value.
-	maxAmt := ch.LocalChanCfg.ChannelConstraints.MaxPendingAmount
+	maxAmt := ch.LocalChanCfg.ChannelStateBounds.MaxPendingAmount
 
 	return ch.LocalChanCfg.MinHTLC, maxAmt, nil
 }

routing/localchans/manager_test.go

@@ -125,14 +125,14 @@ func TestManager(t *testing.T) {
 			return &channeldb.OpenChannel{}, channeldb.ErrChannelNotFound
 		}
 
-		constraints := channeldb.ChannelConstraints{
+		bounds := channeldb.ChannelStateBounds{
 			MaxPendingAmount: maxPendingAmount,
 			MinHTLC:          minHTLC,
 		}
 
 		return &channeldb.OpenChannel{
 			LocalChanCfg: channeldb.ChannelConfig{
-				ChannelConstraints: constraints,
+				ChannelStateBounds: bounds,
 			},
 		}, nil
 	}