Actually clamp the number of detected CPUs to 16.

Previously we said we did, but didn't.

Fixes #19968; bugfix on 0.2.3.1-alpha.

changes/bug19968

@@ -0,0 +1,11 @@
+  o Minor bugfixes (relay):
+    - Do not try to parallelize workers more than 16x without the
+      user explicitly configuring us to do so, even if we do detect more than
+      16 CPU cores. Fixes bug 19968; bugfix on
+      0.2.3.1-alpha.
+
+
+  o Minor bugfixes (testing):
+    - Avoid a unit test failure on systems with over 16 detectable
+      CPU cores. Fixes bug 19968; bugfix on
+      0.2.3.1-alpha.

src/common/compat.c

@@ -2818,6 +2818,7 @@ compute_num_cpus(void)
                  "will not autodetect any more than %d, though.  If you "
                  "want to configure more, set NumCPUs in your torrc",
                  num_cpus, MAX_DETECTABLE_CPUS);
+      num_cpus = MAX_DETECTABLE_CPUS;
       /* LCOV_EXCL_STOP */
     }
   }