Add a helper function to normalize the current version.

We have need to normalize other versions during version negotiation, but
almost all will be post-negotiation. Hopefully later this can be
replaced with a value explicitly stored on the object and we do away
with ssl->version.

Change-Id: I595db9163d0af2e7c083b9a09310179aaa9ac812
Reviewed-on: https://boringssl-review.googlesource.com/6841
Reviewed-by: Adam Langley <alangley@gmail.com>

ssl/internal.h

diff --git a/ssl/internal.h b/ssl/internal.h
index a9f1508..ad76b8c 100644
--- a/ssl/internal.h
+++ b/ssl/internal.h
@@ -1272,7 +1272,11 @@
  *
  * TODO(davidben): To normalize some DTLS-specific code, move away from using
  * the wire version except at API boundaries. */
-uint16_t ssl3_version_from_wire(SSL *ssl, uint16_t wire_version);
+uint16_t ssl3_version_from_wire(const SSL *ssl, uint16_t wire_version);
+
+/* ssl3_protocol_version returns |ssl|'s protocol version. It is an error to
+ * call this function before the version is determined. */
+uint16_t ssl3_protocol_version(const SSL *ssl);
 
 uint32_t ssl_get_algorithm_prf(const SSL *ssl);
 int tls1_parse_peer_sigalgs(SSL *ssl, const CBS *sigalgs);