Add L2 entry deletion support via web

httpd/page_impl.h

@@ -7,6 +7,7 @@ void send_vlan(uint16_t vlan);
 void send_basic_info(void);
 void send_eee(void);
 void send_l2(uint16_t idx);
+void l2_delete(uint16_t idx);
 void send_mirror(void);
 void send_mtu(void);
 void send_config(void);