Write connection info to a BIO instead of stderr.

Make PrintConnectionInfo write to a BIO rather than stderr.
This prepares for writing connection details to the peer.

Change-Id: I88147952712da57f9a2a1e464371075df156741f
Reviewed-on: https://boringssl-review.googlesource.com/20304
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/tool/server.cc b/tool/server.cc
index 1d64933..dc80137 100644
--- a/tool/server.cc
+++ b/tool/server.cc
@@ -306,7 +306,8 @@
     }
 
     fprintf(stderr, "Connected.\n");
-    PrintConnectionInfo(ssl.get());
+    bssl::UniquePtr<BIO> bio_stderr(BIO_new_fp(stderr, BIO_NOCLOSE));
+    PrintConnectionInfo(bio_stderr.get(), ssl.get());
 
     result = TransferData(ssl.get(), sock);
   } while (args_map.count("-loop") != 0);