Ensure relays don't make multiple connections during bootstrap

Relays do not deliberately launch multiple attempts, so the impact of this
bug should be minimal. This fix also defends against bugs like #20499.

Bugfix on 0.2.8.1-alpha.

changes/bug20591

@@ -0,0 +1,3 @@
+  o Minor bugfixes (relay bootstrap):
+    - Ensure relays don't make multiple connections during bootstrap.
+      Fixes bug 20591; bugfix on 0.2.8.1-alpha.

src/or/networkstatus.c

@@ -880,7 +880,7 @@ update_consensus_networkstatus_downloads(time_t now)
     resource = networkstatus_get_flavor_name(i);
 
     /* Check if we already have enough connections in progress */
-    if (we_are_bootstrapping) {
+    if (we_are_bootstrapping && use_multi_conn) {
       max_in_progress_conns =
         options->ClientBootstrapConsensusMaxInProgressTries;
     }