multi: add block cache size config

This commit adds block cache size to the main lnd config along with the
chainreg config.

config.go

@@ -101,6 +101,10 @@ const (
 	// initiated the channel closure.
 	defaultCoopCloseTargetConfs = 6
 
+	// defaultBlockCacheSize is the size (in bytes) of blocks that will be
+	// keep in memory if no size is specified.
+	defaultBlockCacheSize uint64 = 20 * 1024 * 1024 // 20 MB
+
 	// defaultHostSampleInterval is the default amount of time that the
 	// HostAnnouncer will wait between DNS resolutions to check if the
 	// backing IP of a host has changed.
@@ -273,6 +277,8 @@ type Config struct {
 	LtcdMode      *lncfg.Btcd     `group:"ltcd" namespace:"ltcd"`
 	LitecoindMode *lncfg.Bitcoind `group:"litecoind" namespace:"litecoind"`
 
+	BlockCacheSize uint64 `long:"blockcachesize" description:"The maximum capacity of the block cache"`
+
 	Autopilot *lncfg.AutoPilot `group:"Autopilot" namespace:"autopilot"`
 
 	Tor *lncfg.Tor `group:"Tor" namespace:"tor"`
@@ -434,6 +440,7 @@ func DefaultConfig() Config {
 			UserAgentName:    neutrino.UserAgentName,
 			UserAgentVersion: neutrino.UserAgentVersion,
 		},
+		BlockCacheSize:     defaultBlockCacheSize,
 		UnsafeDisconnect:   true,
 		MaxPendingChannels: lncfg.DefaultMaxPendingChannels,
 		NoSeedBackup:       defaultNoSeedBackup,