Fix reference to default protocol.rbf-coop-close configuration in sample-lnd.conf

Modified description regarding the default value for the parameter protocol.rbf-coop-close:

Replaced: "disable" with "enable"

sample-lnd.conf

@@ -1419,7 +1419,7 @@
 ; Set to disable experimental endorsement signaling.
 ; protocol.no-experimental-endorsement=false
 
-; Set to disable support for RBF based coop close.
+; Set to enable support for RBF based coop close.
 ; protocol.rbf-coop-close=false
 
 ; Set to handle messages of a particular type that falls outside of the