Replace some DTLS version checks with SSL_IS_DTLS.

They weren't updated to account for DTLS 1.2.

Change-Id: I81b3bfcb84a46d7b233bb567976a7de37bc46b92
Reviewed-on: https://boringssl-review.googlesource.com/1503
Reviewed-by: Adam Langley <agl@google.com>
4 files changed