Make maximum SSL version configurable through PeerConnectionFactory::Options

This can be used to activate DTLS 1.2 through a command-line flag from Chromium
later.

BUG=chromium:428343
R=jiayl@webrtc.org, juberti@google.com

Review URL: https://webrtc-codereview.appspot.com/54509004

Cr-Commit-Position: refs/heads/master@{#9328}
11 files changed