Update downstream caps/nick/realname before sending MOTD

The MOTD indicates the end of the registration's message burst, and
the server can send arbitrary messages before it.

Update the supported capabilities, the nick and the realname before
MOTD to make it so client logic that runs on MOTD can work with
up-to-date info.

downstream.go

@@ -1187,6 +1187,8 @@ func (dc *downstreamConn) welcome(ctx context.Context) error {
 		dc.isMultiUpstream = true
 	}
 
+	dc.updateSupportedCaps()
+
 	isupport := []string{
 		fmt.Sprintf("CHATHISTORY=%v", chatHistoryLimit),
 		"CASEMAPPING=ascii",
@@ -1249,6 +1251,9 @@ func (dc *downstreamConn) welcome(ctx context.Context) error {
 		})
 	}
 
+	dc.updateNick()
+	dc.updateRealname()
+
 	if motd := dc.user.srv.Config().MOTD; motd != "" && dc.network == nil {
 		for _, msg := range generateMOTD(dc.srv.prefix(), dc.nick, motd) {
 			dc.SendMessage(msg)
@@ -1265,10 +1270,6 @@ func (dc *downstreamConn) welcome(ctx context.Context) error {
 		})
 	}
 
-	dc.updateNick()
-	dc.updateRealname()
-	dc.updateSupportedCaps()
-
 	if dc.caps["soju.im/bouncer-networks-notify"] {
 		dc.SendBatch("soju.im/bouncer-networks", nil, nil, func(batchRef irc.TagValue) {
 			dc.user.forEachNetwork(func(network *network) {