Actually check that the message has the expected type in DTLS.

That might be a reasonable check to make, maybe.

DTLS handshake message reading has a ton of other bugs and needs a complete
rewrite. But let's fix this and get a test in now.

Change-Id: I4981fc302feb9125908bb6161ed1a18288c39e2b
Reviewed-on: https://boringssl-review.googlesource.com/3600
Reviewed-by: Adam Langley <agl@google.com>
4 files changed