Implementing basic LLDP server, should send port_id message

to each port once every 30 seconds.
* Additionally fixes the on-ward passing of LLDP frames through
the switch

The ports on the case are marked 1-8 so this should reflect that
rather than being 0-based

We can send the hostname as well, this can be dynamically allocated

Let's send the model as the system description as well

rtl837x_lldp.h

@@ -0,0 +1,36 @@
+#ifndef _LLDP_H_
+#define _LLDP_H_
+
+#include <stdint.h>
+
+#define LLDP_MIN_ETHERNET_PAYLOAD_LENGTH 46
+#define LLDP_ETHERTYPE       0x88cc
+#define LLDP_ETHERTYPE_LENGTH 2
+#define LLDP_MAX_FRAME       256
+#define LLDP_MAC_ADDR_LEN    6
+#define LLDP_TX_INTERVAL_SEC 30
+
+#define LLDP_PORT_ID_TLV_TYPE 2
+#define LLDP_PORT_ID_TLV_LENGTH 0x02
+#define LLDP_PORT_ID_TLV_SUBTYPE 0x07
+
+#define LLDP_TTL_TLV_TYPE 3
+#define LLDP_TTL_TLV_LENGTH 2
+#define LLDP_TTL_TTL_SECONDS 120
+
+#define LLDP_CHASSIS_ID_TLV_TYPE 1
+#define LLDP_CHASSIS_ID_TLV_LENGTH 7
+#define LLDP_CHASSIS_ID_TLV_SUBTYPE 4
+
+#define LLDP_SYSNAME_TLV_TYPE 5
+#define LLDP_SYSDESC_TLV_TYPE 6
+
+void lldp_init(void) __banked;
+void lldp_tick(void) __banked;
+void lldp_send(void) __banked;
+void lldp_set_addresses(void) __banked;
+void lldp_set_rtl_wrapper(void) __banked;
+void lldp_sysname(uint8_t *p, uint16_t *len) __banked;
+void lldp_sysdesc(uint8_t *p, uint16_t *len) __banked;
+
+#endif