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/library/error.c b/library/error.c
index 0a9baeb..546fa49 100644
--- a/library/error.c
+++ b/library/error.c
@@ -525,6 +525,8 @@
             mbedtls_snprintf( buf, buflen, "SSL - Internal-only message signaling that a message arrived early" );
         if( use_ret == -(MBEDTLS_ERR_SSL_UNEXPECTED_CID) )
             mbedtls_snprintf( buf, buflen, "SSL - An encrypted DTLS-frame with an unexpected CID was received" );
+        if( use_ret == -(MBEDTLS_ERR_SSL_VERSION_MISMATCH) )
+            mbedtls_snprintf( buf, buflen, "SSL - An operation failed due to an unexpected version or configuration" );
         if( use_ret == -(MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS) )
             mbedtls_snprintf( buf, buflen, "SSL - A cryptographic operation is in progress. Try again later" );
 #endif /* MBEDTLS_SSL_TLS_C */
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index cc42171..39ee494 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -9088,8 +9088,7 @@
     if( memcmp( p, ssl_serialized_session_header,
                 sizeof( ssl_serialized_session_header ) ) != 0 )
     {
-        /* A more specific error code might be used here. */
-        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+        return( MBEDTLS_ERR_SSL_VERSION_MISMATCH );
     }
     p += sizeof( ssl_serialized_session_header );