multi: Set upfront shutdown from open and accept chanel messages

This commit gets upfront shutdown scripts from openchannel and
acceptchannel wire messages sent from our peer and sets upfront
shutdown scripts in our open and accept channel messages when
the remote peer supports option upfront shutdown and we have
the feature enabled.

server.go

@@ -3088,6 +3088,10 @@ type openChanReq struct {
 	// output selected to fund the channel should satisfy.
 	minConfs int32
 
+	// shutdownScript is an optional upfront shutdown script for the channel.
+	// This value is optional, so may be nil.
+	shutdownScript lnwire.DeliveryAddress
+
 	// TODO(roasbeef): add ability to specify channel constraints as well
 
 	updates chan *lnrpc.OpenStatusUpdate