Lower the default path bias notice rate to 40%.

I saw 72% on a test run with 26 circuits. 70% might be a little close to the
line. That, or min_circs is too low and we need to be more patient. We still
need to test/simulate more.

src/or/circuitbuild.c

@@ -2578,7 +2578,7 @@ pathbias_get_min_circs(const or_options_t *options)
 static double
 pathbias_get_notice_rate(const or_options_t *options)
 {
-#define DFLT_PATH_BIAS_NOTICE_PCT 70
+#define DFLT_PATH_BIAS_NOTICE_PCT 40
   if (options->PathBiasNoticeRate >= 0.0)
     return options->PathBiasNoticeRate;
   else