Fix a problem where, when ndhc is waiting for an arp packet, an arp packet

is received that is discarded by ndhc's basic checks and provokes a busy
loop in the main program loop because epoll_wait() constantly sees data that
is never drained from the socket buffer since arp_offset exceeds the
maximum size of an ARP packet and would overflow the packet buffer.

ndhc/arp.c

@@ -302,14 +302,15 @@ void handle_arp_response(struct client_state_t *cs)
             arpreply_offset += r;
     }
 
-    if (arpreply_offset < ARP_MSG_SIZE) {
+
-        log_warning("arp: Received short ARP message -- ignoring");
+    if (arpreply_offset < ARP_MSG_SIZE)
+        return;
+
+    if (!arp_validate(&arpreply)) {
+        arpreply_clear();
         return;
     }
 
-    if (!arp_validate(&arpreply))
-        return;
-
     ++arp_packet_num;
     switch (cs->dhcpState) {
     case DS_ARP_CHECK: