lnwallet+funding+lnd: add new config option for min accepted channel size

In this commit we add a new command line option (and a sane default) to
allow users to specify the *smallest* inbound channel that they'll
accept. Having a higher-ish limit lets users limit their channels, and
also avoid a series of very low value "spam" channels.

The new option is --minchansize, and expressed in satoshis. If we
receive an inbound channel request for a value smaller than this, then
we'll immediately reject it.

config.go

@@ -195,8 +195,9 @@ type config struct {
 
 	TrickleDelay int `long:"trickledelay" description:"Time in milliseconds between each release of announcements to the network"`
 
-	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"`
+	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"`
 
 	net torsvc.Net
 }
@@ -264,6 +265,7 @@ func loadConfig() (*config, error) {
 		TrickleDelay: defaultTrickleDelay,
 		Alias:        defaultAlias,
 		Color:        defaultColor,
+		MinChanSize:  int64(minChanFundingSize),
 	}
 
 	// Pre-parse the command line options to pick up an alternative config