Added Who-Is-Router process for Notification Class recipient unknown router addresses. (#1243)

* Added Who-Is-Router-To-Network process in basic Notification Class when recipient address is missing the router MAC address.

* Added buffer_length parameter to octet string buffer decode functions

* Fixed BACnet address handling for I-Am-Router address updating the recipient list address for the next hop router.

* Changed VMAC encoding and decoding to use octet string buffer API to reduce stack RAM.

src/bacnet/bacdest.c

@@ -125,6 +125,28 @@ void bacnet_recipient_address_set(
     }
 }
 
+/**
+ * @brief Inspect the BACnetRecipient data structure for valid router address
+ * @param recipient - BACnetRecipient structure
+ * @return true if BACnetRecipient is a valid address
+ */
+bool bacnet_recipient_address_router_unknown(const BACNET_RECIPIENT *recipient)
+{
+    bool status = false;
+
+    if (recipient) {
+        if ((recipient->tag == BACNET_RECIPIENT_TAG_ADDRESS) &&
+            (recipient->type.address.net != 0) &&
+            (recipient->type.address.net != BACNET_BROADCAST_NETWORK) &&
+            (recipient->type.address.len != 0) &&
+            (recipient->type.address.mac_len == 0)) {
+            status = true;
+        }
+    }
+
+    return status;
+}
+
 /**
  * @brief Copy the BACnetRecipient complex data from src to dest
  * @param src - BACnetRecipient 1 structure