downstream: improve grouping of downstreamConn fields

downstream.go

@@ -300,23 +300,24 @@ type downstreamConn struct {
 
 	id uint64
 
+	// These don't change after connection registration
 	registered      bool
 	user            *user
+	network         *network // can be nil
+	isMultiUpstream bool
+	clientName      string
+
 	nick     string
 	nickCM   string
-	clientName      string
 	realname string
 	hostname string
 	account  string // RPL_LOGGEDIN/OUT state
-	network         *network // can be nil
-	isMultiUpstream bool
-
-	registration *downstreamRegistration // nil after RPL_WELCOME
 
 	negotiatingCaps bool
 	capVersion      int
 	caps            capRegistry
 	sasl            *downstreamSASL
+	registration    *downstreamRegistration // nil after RPL_WELCOME
 
 	lastBatchRef uint64