server+lncfg: add new config flag to enable wumbo channels

In this commit, we add a new config flag to enable wumbo channels, with
the default being that nodes reject all wumbo channel attempts.

lncfg/protocol.go

@@ -12,4 +12,15 @@ type ProtocolOptions struct {
 	// ExperimentalProtocol is a sub-config that houses any experimental
 	// protocol features that also require a build-tag to activate.
 	ExperimentalProtocol
+
+	// WumboChans should be set if we want to enable support for wumbo
+	// (channels larger than 0.16 BTC) channels, which is the opposite of
+	// mini.
+	WumboChans bool `long:"wumbo-channels" description:"if set, then lnd will create and accept requests for channels larger chan 0.16 BTC"`
+}
+
+// Wumbo returns true if lnd should permit the creation and acceptance of wumbo
+// channels.
+func (l *ProtocolOptions) Wumbo() bool {
+	return l.WumboChans
 }