ICMP: Treat genuine ICMP diagnostic PDU for UDP as failure

Posix support only for unicast client requests.

ICMP disgnostic messages are ignored on server sessions.

include/coap3/coap_dgrm_internal.h

@@ -21,6 +21,14 @@
 extern "C" {
 #endif
 
+typedef struct coap_icmp_info_t {
+  uint32_t length;
+  uint8_t cmsg_level;
+  uint8_t ee_origin;
+  uint8_t ee_type;
+  uint8_t ee_code;
+} coap_icmp_info_t;
+
 /**
  * @ingroup internal_api
  * @defgroup dgrm Datagram (UDP) Support

include/coap3/coap_session_internal.h

@@ -260,6 +260,10 @@ struct coap_session_t {
   coap_tick_t last_tx;            /**< Last time a ratelimited packet is sent */
   uint8_t is_rate_limiting;       /**< Currently NON rate limiting */
   uint32_t ping_failed;           /**< Ping failure count */
+#ifdef HAVE_LINUX_ERRQUEUE_H
+  coap_str_const_t *last_data_write; /**< Last sent data to check against ICMP
+                                          responses */
+#endif /* HAVE_LINUX_ERRQUEUE_H */
 };
 
 #if COAP_SERVER_SUPPORT