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>