lncfg+sample-lnd.conf: add --neutrino.validatechannels

sample-lnd.conf

@@ -460,6 +460,14 @@ bitcoin.node=btcd
 ; Used to help identify ourselves to other bitcoin peers (default: 0.11.0-beta).
 ; neutrino.useragentversion=0.11.0-beta
 
+; Validate every channel in the graph during sync by downloading the containing
+; block. This is the inverse of routing.assumechanvalid, meaning that for
+; Neutrino the validation is turned off by default for massively increased graph
+; sync performance. This speedup comes at the risk of using an unvalidated view
+; of the network for routing. Overwrites the value of routing.assumechanvalid if
+; Neutrino is used. (default: false)
+; neutrino.validatechannels=false
+
 ; Skip checking channel spentness and existence during graph validation for
 ; neutrino. Enabling this option means that neutrino nodes will not need to
 ; perform long rescans which block initial usage of the daemon, but comes at