Revert "Remove obsolete workaround in dirserv_thinks_router_is_hs_dir()"

Fixes #15850, part of #15801. Change file is added by this commit. The
original comment in the reverted commit is removed because right now we
*need* a DirPort until #15849 is implemented so no doubt nor confusion there
anymore.

This reverts commit 80bed1ac96a3035f8c55ddced5528f0d7d16d386.

Signed-off-by: David Goulet <dgoulet@ev0ke.net>

changes/bug15850

@@ -0,0 +1,4 @@
+  o Major bugfix
+    - Revert commit that made directory authority assign the HSDir flag to
+      relay without a DirPort which is bad because relay can't handle
+      BEGIN_DIR cells. Fixes #15850. Bugfix on tor-0.2.6.3-alpha;

src/or/dirserv.c

@@ -1305,7 +1305,7 @@ dirserv_thinks_router_is_hs_dir(const routerinfo_t *router,
   else
     uptime = real_uptime(router, now);
 
-  return (router->wants_to_be_hs_dir &&
+  return (router->wants_to_be_hs_dir && router->dir_port &&
           uptime >= get_options()->MinUptimeHidServDirectoryV2 &&
           router_is_active(router, node, now));
 }