rpc: add new commitment_type field to OpenChannelRequest

This field will be examined later down the stack along with the set of
feature bits to determine if explicit channel commitment type
negotiation is possible or not.

funding/manager.go

@@ -240,6 +240,11 @@ type InitFundingMsg struct {
 	// protocol.
 	PendingChanID [32]byte
 
+	// ChannelType allows the caller to use an explicit channel type for the
+	// funding negotiation. This type will only be observed if BOTH sides
+	// support explicit channel type negotiation.
+	ChannelType *lnwire.ChannelType
+
 	// Updates is a channel which updates to the opening status of the channel
 	// are sent on.
 	Updates chan *lnrpc.OpenStatusUpdate