lnd: expose user agent name as config option

Expose the neutrino `UserAgentName` config option. This can be set by
starting lnd with the `--neutrino.useragentname=` flag.

chainregistry.go

@@ -785,6 +785,7 @@ func initNeutrinoBackend(cfg *Config, chainDir string) (*neutrino.ChainService,
 
 	neutrino.MaxPeers = 8
 	neutrino.BanDuration = time.Hour * 48
+	neutrino.UserAgentName = cfg.NeutrinoMode.UserAgentName
 
 	neutrinoCS, err := neutrino.NewChainService(config)
 	if err != nil {

docs/INSTALL.md

@@ -197,6 +197,7 @@ neutrino:
       --neutrino.maxpeers=                                    Max number of inbound and outbound peers
       --neutrino.banduration=                                 How long to ban misbehaving peers.  Valid time units are {s, m, h}.  Minimum 1 second
       --neutrino.banthreshold=                                Maximum allowed ban score before disconnecting and banning misbehaving peers.
+      --neutrino.useragentname=                               Used to help identify ourselves to other bitcoin peers.
 ```
 
 ## Bitcoind Options

lncfg/neutrino.go

@@ -12,4 +12,5 @@ type Neutrino struct {
 	BanThreshold       uint32        `long:"banthreshold" description:"Maximum allowed ban score before disconnecting and banning misbehaving peers."`
 	FeeURL             string        `long:"feeurl" description:"Optional URL for fee estimation. If a URL is not specified, static fees will be used for estimation."`
 	AssertFilterHeader string        `long:"assertfilterheader" description:"Optional filter header in height:hash format to assert the state of neutrino's filter header chain on startup. If the assertion does not hold, then the filter header chain will be re-synced from the genesis block."`
+	UserAgentName      string        `long:"useragentname" description:"Used to help identify ourselves to other bitcoin peers"`
 }