Add --fast-dns-retry option.

This gives dnsmasq the ability to originate retries for upstream DNS
queries itself, rather than relying on the downstream client. This is
most useful when doing DNSSEC over unreliable upstream network. It
comes with some cost in memory usage and network bandwidth.

src/option.c

@@ -182,6 +182,7 @@ struct myoption {
 #define LOPT_CONF_OPT      373
 #define LOPT_CONF_SCRIPT   374
 #define LOPT_RANDPORT_LIM  375
+#define LOPT_FAST_RETRY    376
 
 #ifdef HAVE_GETOPT_LONG
 static const struct option opts[] =  
@@ -368,6 +369,7 @@ static const struct myoption opts[] =
     { "umbrella", 2, 0, LOPT_UMBRELLA },
     { "quiet-tftp", 0, 0, LOPT_QUIET_TFTP },
     { "port-limit", 1, 0, LOPT_RANDPORT_LIM },
+    { "fast-dns-retry", 1, 0, LOPT_FAST_RETRY },
     { NULL, 0, 0, 0 }
   };
 
@@ -446,6 +448,7 @@ static struct {
   { LOPT_MAXTTL, ARG_ONE, "<integer>", gettext_noop("Specify time-to-live in seconds for maximum TTL to send to clients."), NULL },
   { LOPT_MAXCTTL, ARG_ONE, "<integer>", gettext_noop("Specify time-to-live ceiling for cache."), NULL },
   { LOPT_MINCTTL, ARG_ONE, "<integer>", gettext_noop("Specify time-to-live floor for cache."), NULL },
+  { LOPT_FAST_RETRY, ARG_ONE, "<milliseconds>", gettext_noop("Retry DNS queries after this many milliseconds."), NULL},
   { 'u', ARG_ONE, "<username>", gettext_noop("Change to this user after startup. (defaults to %s)."), CHUSER }, 
   { 'U', ARG_DUP, "set:<tag>,<class>", gettext_noop("Map DHCP vendor class to tag."), NULL },
   { 'v', 0, NULL, gettext_noop("Display dnsmasq version and copyright information."), NULL },
@@ -3222,6 +3225,15 @@ static int one_opt(int option, char *arg, char *errstr, char *gen_err, int comma
 	  daemon->local_ttl = (unsigned long)ttl;
 	break;
       }
+
+    case LOPT_FAST_RETRY:
+      {
+	int retry;
+      	if (!atoi_check(arg, &retry) || retry < 500)
+	  ret_err(gen_err);
+	daemon->fast_retry_time = retry;
+	break;
+      }
       
 #ifdef HAVE_DHCP
     case 'X': /* --dhcp-lease-max */
@@ -5503,7 +5515,7 @@ void read_opts(int argc, char **argv, char *compile_opts)
   daemon->soa_retry = SOA_RETRY;
   daemon->soa_expiry = SOA_EXPIRY;
   daemon->randport_limit = 1;
-  
+    
 #ifndef NO_ID
   add_txt("version.bind", "dnsmasq-" VERSION, 0 );
   add_txt("authors.bind", "Simon Kelley", 0);