Move ssl_set_fallback() to work on conf

Initially thought it would be per-connection, but since max_version is in conf
too, and you need to lower that for a fallback connection, the fallback flag
should be in the same place
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 354cc5a..bbc8838 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -733,7 +733,7 @@
 
     /* Some versions of OpenSSL don't handle it correctly if not at end */
 #if defined(MBEDTLS_SSL_FALLBACK_SCSV)
-    if( ssl->fallback == MBEDTLS_SSL_IS_FALLBACK )
+    if( ssl->conf->fallback == MBEDTLS_SSL_IS_FALLBACK )
     {
         MBEDTLS_SSL_DEBUG_MSG( 3, ( "adding FALLBACK_SCSV" ) );
         *p++ = (unsigned char)( MBEDTLS_SSL_FALLBACK_SCSV_VALUE >> 8 );