Fix <= TLS1.2 break

Changing the value of SSL_MAX_MASTER_KEY_LENGTH had some unexpected
side effects in the <=TLS1.2 code which apparently relies on this being
48 for interoperability. Therefore create a new define for the TLSv1.3
resumption master secret which can be up to 64 bytes.

Found through the boring test suite.
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2259)

include/openssl/ssl.h

@@ -76,7 +76,8 @@ extern "C" {
 
 # define SSL_MIN_RSA_MODULUS_LENGTH_IN_BYTES     (512/8)
 # define SSL_MAX_KEY_ARG_LENGTH                  8
-# define SSL_MAX_MASTER_KEY_LENGTH               64
+# define SSL_MAX_MASTER_KEY_LENGTH               48
+# define TLS13_MAX_RESUMPTION_MASTER_LENGTH      64
 
 /* The maximum number of encrypt/decrypt pipelines we can support */
 # define SSL_MAX_PIPELINES  32

ssl/ssl_asn1.c

@@ -294,7 +294,7 @@ SSL_SESSION *d2i_SSL_SESSION(SSL_SESSION **a, const unsigned char **pp,
         goto err;
 
     if (!ssl_session_memcpy(ret->master_key, &tmpl,
-                            as->master_key, SSL_MAX_MASTER_KEY_LENGTH))
+                            as->master_key, TLS13_MAX_RESUMPTION_MASTER_LENGTH))
         goto err;
 
     ret->master_key_length = tmpl;

ssl/ssl_locl.h

@@ -515,7 +515,7 @@ struct ssl_session_st {
      * For <=TLS1.2 this is the master_key. For TLS1.3 this is the resumption
      * master secret
      */
-    unsigned char master_key[SSL_MAX_MASTER_KEY_LENGTH];
+    unsigned char master_key[TLS13_MAX_RESUMPTION_MASTER_LENGTH];
     /* session_id - valid? */
     size_t session_id_length;
     unsigned char session_id[SSL_MAX_SSL_SESSION_ID_LENGTH];