multi: cap anchors feerate at configurable maximum

This commit caps the update fee the initiator will send when the anchors
channel type is used. We do not limit anything on the receiver side.

10 sat/vbyte is the current default max fee rate we use. This should be
enough to ensure propagation before anchoring down the commitment
transaction.

server.go

@@ -1185,6 +1185,8 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 		NotifyPendingOpenChannelEvent: s.channelNotifier.NotifyPendingOpenChannelEvent,
 		EnableUpfrontShutdown:         cfg.EnableUpfrontShutdown,
 		RegisteredChains:              cfg.registeredChains,
+		MaxAnchorsCommitFeeRate: chainfee.SatPerKVByte(
+			s.cfg.MaxCommitFeeRateAnchors * 1000).FeePerKWeight(),
 	})
 	if err != nil {
 		return nil, err
@@ -3119,7 +3121,9 @@ func (s *server) peerConnected(conn net.Conn, connReq *connmgr.ConnReq,
 		UnsafeReplay:            s.cfg.UnsafeReplay,
 		MaxOutgoingCltvExpiry:   s.cfg.MaxOutgoingCltvExpiry,
 		MaxChannelFeeAllocation: s.cfg.MaxChannelFeeAllocation,
-		Quit:                    s.quit,
+		MaxAnchorsCommitFeeRate: chainfee.SatPerKVByte(
+			s.cfg.MaxCommitFeeRateAnchors * 1000).FeePerKWeight(),
+		Quit: s.quit,
 	}
 
 	copy(pCfg.PubKeyBytes[:], peerAddr.IdentityKey.SerializeCompressed())