[3242] Log when received message is not supported.

src/bin/dhcp4/dhcp4_messages.mes

@@ -141,6 +141,12 @@ This debug message indicates that the message type carried in DHCPv4 option
 on the IANA website: http://www.iana.org/assignments/bootp-dhcp-parameters/bootp-dhcp-parameters.xhtml#message-type-53.
 The message will not be processed by the server.
 
+% DHCP4_UNSUPPORTED_RCVD_PACKET_TYPE received message (transaction id %1), having type %2 is not supported
+This debug message indicates that the message type carried in DHCPv4 option
+53 is valid but the message will not be processed by the server. This includes
+messages being normally sent by the server to the client, such as Offer, ACK,
+NAK etc.
+
 % DHCP4_LEASE_ADVERT lease %1 advertised (client client-id %2, hwaddr %3)
 This debug message indicates that the server successfully advertised
 a lease. It is up to the client to choose one server out of othe advertised

src/bin/dhcp4/dhcp4_srv.cc

@@ -1629,6 +1629,10 @@ Dhcpv4Srv::acceptMessageType(const Pkt4Ptr& query) const {
     if ((type != DHCPDISCOVER) && (type != DHCPREQUEST) &&
         (type != DHCPRELEASE) && (type != DHCPDECLINE) &&
         (type != DHCPINFORM)) {
+        LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL,
+                  DHCP4_UNSUPPORTED_RCVD_PACKET_TYPE)
+            .arg(type)
+            .arg(query->getTransid());
         return (false);
     }