Guard RSA-only max_major/minor_ver fields from SSL handshake params

The fields
- mbedtls_ssl_handshake_params::max_major_ver,
- mbedtls_ssl_handshake_params::max_minor_ver
are used only for server-side RSA-based key exchanges
can be removed otherwise.
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index 87fe4c9..660b30f 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -1110,8 +1110,12 @@
         return( MBEDTLS_ERR_SSL_BAD_HS_PROTOCOL_VERSION );
     }
 
+#if defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED) ||        \
+    defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED)
     ssl->handshake->max_major_ver = buf[3];
     ssl->handshake->max_minor_ver = buf[4];
+#endif /* MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED ||
+          MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED */
 
     if( ( ret = mbedtls_ssl_fetch_input( ssl, 2 + n ) ) != 0 )
     {
@@ -1630,8 +1634,12 @@
                                   ssl->conf->transport,
                                   buf );
 
+#if defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED) ||        \
+    defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED)
         ssl->handshake->max_major_ver = major_ver;
         ssl->handshake->max_minor_ver = minor_ver;
+#endif /* MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED ||
+          MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED */
 
         if( major_ver < mbedtls_ssl_conf_get_min_major_ver( ssl->conf ) ||
             minor_ver < mbedtls_ssl_conf_get_min_minor_ver( ssl->conf ) )