Add reading of RSTP-CNF packets and send own CNF packets

This reads RSTP configuration packages and updates the
state information about the believed Root-bridge. New
RSTP packages are sent with the updated information.

rtl837x_stp.h

@@ -2,6 +2,11 @@
 #define _RTL837X_STP_H_
 
 #include <stdint.h>
-void stp_cnf_send(uint8_t port) __banked;
+void stp_in(void) __banked;
+void stp_setup(void) __banked;
+void stp_timers(void) __banked;
+void stp_off(void) __banked;
+
+#define TIME_HELLO 0x200 // 2 sec
 
 #endif