--dhcp-reply-delay option to workaround PXE client bugs.

Adds option to delay replying to DHCP packets by one or more seconds.
This provides a workaround for a PXE boot firmware implementation
that has a bug causing it to fail if it receives a (proxy) DHCP
reply instantly.

On Linux it looks up the exact receive time of the UDP packet with
the SIOCGSTAMP ioctl to prevent multiple delays if multiple packets
come in around the same time.

src/option.c

@@ -159,6 +159,7 @@ struct myoption {
 #define LOPT_SCRIPT_ARP    347
 #define LOPT_DHCPTTL       348
 #define LOPT_TFTP_MTU      349
+#define LOPT_REPLY_DELAY   350
  
 #ifdef HAVE_GETOPT_LONG
 static const struct option opts[] =  
@@ -323,6 +324,7 @@ static const struct myoption opts[] =
     { "dns-loop-detect", 0, 0, LOPT_LOOP_DETECT },
     { "script-arp", 0, 0, LOPT_SCRIPT_ARP },
     { "dhcp-ttl", 1, 0 , LOPT_DHCPTTL },
+    { "dhcp-reply-delay", 1, 0, LOPT_REPLY_DELAY },
     { NULL, 0, 0, 0 }
   };
 
@@ -494,6 +496,7 @@ static struct {
   { LOPT_LOOP_DETECT, OPT_LOOP_DETECT, NULL, gettext_noop("Detect and remove DNS forwarding loops."), NULL },
   { LOPT_IGNORE_ADDR, ARG_DUP, "<ipaddr>", gettext_noop("Ignore DNS responses containing ipaddr."), NULL }, 
   { LOPT_DHCPTTL, ARG_ONE, "<ttl>", gettext_noop("Set TTL in DNS responses with DHCP-derived addresses."), NULL }, 
+  { LOPT_REPLY_DELAY, ARG_ONE, "<integer>", gettext_noop("Delay DHCP replies for at least number of seconds."), NULL },
   { 0, 0, NULL, NULL, NULL }
 }; 
 
@@ -3317,11 +3320,43 @@ static int one_opt(int option, char *arg, char *errstr, char *gen_err, int comma
 	break;
       }
 
+    case LOPT_REPLY_DELAY: /* --dhcp-reply-delay */
+      {
+	struct dhcp_netid *id = NULL;
+	while (is_tag_prefix(arg))
+	  {
+	    struct dhcp_netid *newid = opt_malloc(sizeof(struct dhcp_netid));
+	    newid->next = id;
+	    id = newid;
+	    comma = split(arg);
+	    newid->net = opt_string_alloc(arg+4);
+	    arg = comma;
+	  };
+	
+	if (!arg)
+	  ret_err(gen_err);
+	else
+	  {
+	    struct delay_config *new;
+	    int delay;
+	    if (!atoi_check(arg, &delay))
+              ret_err(gen_err);
+	    
+	    new = opt_malloc(sizeof(struct delay_config));
+	    new->delay = delay;
+	    new->netid = id;
+            new->next = daemon->delay_conf;
+            daemon->delay_conf = new;
+	  }
+	
+	break;
+      }
+      
     case LOPT_PXE_PROMT:  /* --pxe-prompt */
        {
 	 struct dhcp_opt *new = opt_malloc(sizeof(struct dhcp_opt));
 	 int timeout;
-
+	 
 	 new->netid = NULL;
 	 new->opt = 10; /* PXE_MENU_PROMPT */