httpd: do not initialise tstate through uip_conn

uip_init() does not set uip_conn, and httpd_init() runs right after it, so
the assignment went through a pointer nothing had assigned yet.

It has stayed invisible because the startup code does clear xdata: uip_conn
is NULL rather than garbage, appstate sits 28 bytes into struct uip_conn, and
the byte therefore lands at xdata 0x1C. With the current map that is inside
the command line buffer, at an offset nothing reads while the line is empty,
and cmd_editor_init() runs later anyway.

Nothing is broken today, but it is a write to an address that has nothing to
do with the state being set, and it moves the moment the struct grows or the
map shifts. Address the connection directly.

httpd/httpd.c

@@ -101,10 +101,11 @@ inline uint8_t is_separator(uint8_t c)
 void httpd_init(void) __banked
 {
 	config_upload = 0; // xdata is not zeroed by the startup code
-	__xdata struct httpd_state * __xdata s = &(uip_conn->appstate);
 	// Start listening to port 80
 	uip_listen(HTONS(80));
-	s->tstate = TSTATE_CLOSED;
+	// Not through uip_conn: it only points at a connection while uIP is
+	// handling one, and nothing has set it yet at init time.
+	uip_conns[0].appstate.tstate = TSTATE_CLOSED;
 	fw_reset_pending = 0; // xdata is not zeroed by the startup code
 }