ircd/listener: return a fatal TLS alert for early rejected TLS clients

This is in furtherance of commit 3fdf26a which added
functionality to reply with a TLS record layer alert for D-Lined TLS
clients. It turns out that there are other plaintext error messages
in this same function that should receive the same treatment.

Also move another error string to a variable and use a compile-time
optimised-out strlen for it too, to use the same approach as an
existing error string.

Finally, use a different alert (internal_error) for the case where
IRCd is simply unable to accept more connections.

ircd/listener.c

@@ -581,13 +581,19 @@ accept_precallback(rb_fde_t *F, struct sockaddr *addr, rb_socklen_t addrlen, voi
 	static time_t last_oper_notice = 0;
 	int len;
 
+	static const char *allinuse = "ERROR :All connections in use\r\n";
 	static const char *toofast = "ERROR :Reconnecting too fast, throttled.\r\n";
 
-	static const unsigned char sslerrcode[] = {
+	static const unsigned char ssldeniederrcode[] = {
 		// SSLv3.0 Fatal Alert: Access Denied
 		0x15, 0x03, 0x00, 0x00, 0x02, 0x02, 0x31
 	};
 
+	static const unsigned char sslinternalerrcode[] = {
+		// SSLv3.0 Fatal Alert: Internal Error
+		0x15, 0x03, 0x00, 0x00, 0x02, 0x02, 0x50
+	};
+
 	if(listener->ssl && (!ircd_ssl_ok || !get_ssld_count()))
 	{
 		rb_close(F);
@@ -608,7 +614,11 @@ accept_precallback(rb_fde_t *F, struct sockaddr *addr, rb_socklen_t addrlen, voi
 			last_oper_notice = rb_current_time();
 		}
 
-		rb_write(F, "ERROR :All connections in use\r\n", 31);
+		if(listener->ssl)
+			rb_write(F, sslinternalerrcode, sizeof(sslinternalerrcode));
+		else
+			rb_write(F, allinuse, strlen(allinuse));
+
 		rb_close(F);
 		return 0;
 	}
@@ -625,7 +635,7 @@ accept_precallback(rb_fde_t *F, struct sockaddr *addr, rb_socklen_t addrlen, voi
 
 		if(listener->ssl)
 		{
-			rb_write(F, sslerrcode, sizeof(sslerrcode));
+			rb_write(F, ssldeniederrcode, sizeof(ssldeniederrcode));
 		}
 		else if(ConfigFileEntry.dline_with_reason)
 		{
@@ -656,7 +666,11 @@ accept_precallback(rb_fde_t *F, struct sockaddr *addr, rb_socklen_t addrlen, voi
 
 	if(throttle_add(addr))
 	{
-		rb_write(F, toofast, strlen(toofast));
+		if(listener->ssl)
+			rb_write(F, ssldeniederrcode, sizeof(ssldeniederrcode));
+		else
+			rb_write(F, toofast, strlen(toofast));
+
 		rb_close(F);
 		return 0;
 	}