Channel ID is incompatible with 0-RTT, so we gracefully decline 0-RTT
as a server and forbid their combination as a client. We'll keep this
logic around until Channel ID is removed.

Channel ID will be replaced by tokbind which currently uses custom
extensions. Those will need additional logic to work with 0-RTT.
This is not implemented yet so, for now, fail if both are ever
configured together at all. A later change will allow the two to
combine.

BUG=183

Change-Id: I46c5ba883ccd47930349691fb08074a1fab13d5f
Reviewed-on: https://boringssl-review.googlesource.com/14370
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>