Introduce specific error for ver/cfg mismatch on deserialization

This commit introduces a new SSL error code

  `MBEDTLS_ERR_SSL_VERSION_MISMATCH`

which can be used to indicate operation failure due to a
mismatch of version or configuration.

It is put to use in the implementation of `mbedtls_ssl_session_load()`
to signal the attempt to de-serialize a session which has been serialized
in a build of Mbed TLS using a different version or configuration.
diff --git a/include/mbedtls/error.h b/include/mbedtls/error.h
index 765fd42..31f294f 100644
--- a/include/mbedtls/error.h
+++ b/include/mbedtls/error.h
@@ -100,6 +100,7 @@
  * ECP       4   10 (Started from top)
  * MD        5   5
  * HKDF      5   1 (Started from top)
+ * SSL       5   1 (Started from 0x5F00)
  * CIPHER    6   8 (Started from 0x6080)
  * SSL       6   24 (Started from top, plus 0x6000)
  * SSL       7   32