add new max channel size config option

- let users specify their MAXIMUM WUMBO with new config option which sets the maximum channel size lnd will accept
- current implementation is a simple check by the fundingManager rather than anything to do with the ChannelAcceptor
- Add test cases which verify that maximum channel limit is respected for wumbo/non-wumbo channels
- use --maxchansize 0 value to distinguish set/unset config. If user sets max value to 0 it will not do anything as 0 is currently used to indicate to the funding manager that the limit should not be enforced. This seems justifiable since --maxchansize=0 doesn't seem to make sense at first glance.
- add integration test case to ensure that config parsing and valiation is proper. I simplified the funding managers check electing to rely on config.go to correctly parse and set up either i) non wumbo default limit of 0.16 BTC OR ii) wumbo default soft limit of 10 BTC

Addresses: https://github.com/lightningnetwork/lnd/issues/4557

config.go

@@ -240,6 +240,7 @@ type Config struct {
 	Alias                         string        `long:"alias" description:"The node alias. Used as a moniker by peers and intelligence services"`
 	Color                         string        `long:"color" description:"The color of the node in hex format (i.e. '#3399FF'). Used to customize node appearance in intelligence services"`
 	MinChanSize                   int64         `long:"minchansize" description:"The smallest channel size (in satoshis) that we should accept. Incoming channels smaller than this will be rejected"`
+	MaxChanSize                   int64         `long:"maxchansize" description:"The largest channel size (in satoshis) that we should accept. Incoming channels larger than this will be rejected"`
 
 	DefaultRemoteMaxHtlcs uint16 `long:"default-remote-max-htlcs" description:"The default max_htlc applied when opening or accepting channels. This value limits the number of concurrent HTLCs that the remote party can add to the commitment. The maximum possible value is 483."`
 
@@ -387,6 +388,7 @@ func DefaultConfig() Config {
 		Alias:                         defaultAlias,
 		Color:                         defaultColor,
 		MinChanSize:                   int64(minChanFundingSize),
+		MaxChanSize:                   int64(0),
 		DefaultRemoteMaxHtlcs:         defaultRemoteMaxHtlcs,
 		NumGraphSyncPeers:             defaultMinPeers,
 		HistoricalSyncInterval:        discovery.DefaultHistoricalSyncInterval,
@@ -610,7 +612,7 @@ func ValidateConfig(cfg Config, usageMessage string) (*Config, error) {
 	}
 
 	// Ensure that the specified values for the min and max channel size
-	// don't are within the bounds of the normal chan size constraints.
+	// are within the bounds of the normal chan size constraints.
 	if cfg.Autopilot.MinChannelSize < int64(minChanFundingSize) {
 		cfg.Autopilot.MinChannelSize = int64(minChanFundingSize)
 	}
@@ -622,6 +624,38 @@ func ValidateConfig(cfg Config, usageMessage string) (*Config, error) {
 		return nil, err
 	}
 
+	// Ensure that --maxchansize is properly handled when set by user.
+	// For non-Wumbo channels this limit remains 16777215 satoshis by default
+	// as specified in BOLT-02. For wumbo channels this limit is 1,000,000,000.
+	// satoshis (10 BTC). Always enforce --maxchansize explicitly set by user.
+	// If unset (marked by 0 value), then enforce proper default.
+	if cfg.MaxChanSize == 0 {
+		if cfg.ProtocolOptions.Wumbo() {
+			cfg.MaxChanSize = int64(MaxBtcFundingAmountWumbo)
+		} else {
+			cfg.MaxChanSize = int64(MaxBtcFundingAmount)
+		}
+	}
+
+	// Ensure that the user specified values for the min and max channel
+	// size make sense.
+	if cfg.MaxChanSize < cfg.MinChanSize {
+		return nil, fmt.Errorf("invalid channel size parameters: "+
+			"max channel size %v, must be no less than min chan size %v",
+			cfg.MaxChanSize, cfg.MinChanSize,
+		)
+	}
+
+	// Don't allow superflous --maxchansize greater than
+	// BOLT 02 soft-limit for non-wumbo channel
+	if !cfg.ProtocolOptions.Wumbo() && cfg.MaxChanSize > int64(MaxFundingAmount) {
+		return nil, fmt.Errorf("invalid channel size parameters: "+
+			"maximum channel size %v is greater than maximum non-wumbo"+
+			" channel size %v",
+			cfg.MaxChanSize, MaxFundingAmount,
+		)
+	}
+
 	// Ensure a valid max channel fee allocation was set.
 	if cfg.MaxChannelFeeAllocation <= 0 || cfg.MaxChannelFeeAllocation > 1 {
 		return nil, fmt.Errorf("invalid max channel fee allocation: "+