Change requirements for setting timer callback

The code wants timer callbacks to be set (checked in fetch_input()), and can't
easily check whether we're using nbio, so it seems easier to require the
callbacks to be always set rather than only with nbio as was previously done.
diff --git a/programs/ssl/ssl_server2.c b/programs/ssl/ssl_server2.c
index bf209e8..b2c140f 100644
--- a/programs/ssl/ssl_server2.c
+++ b/programs/ssl/ssl_server2.c
@@ -3600,17 +3600,14 @@
                             opt.nbio == 0 ? mbedtls_net_recv_timeout : NULL );
 
 #if defined(MBEDTLS_TIMING_C)
-            if( opt.nbio != 0 && opt.read_timeout != 0 )
-            {
 #if !defined(MBEDTLS_SSL_CONF_SET_TIMER) && \
     !defined(MBEDTLS_SSL_CONF_GET_TIMER)
-                mbedtls_ssl_set_timer_cb( &ssl, &timer,
-                                          mbedtls_timing_set_delay,
-                                          mbedtls_timing_get_delay );
+            mbedtls_ssl_set_timer_cb( &ssl, &timer,
+                                      mbedtls_timing_set_delay,
+                                      mbedtls_timing_get_delay );
 #else
-                mbedtls_ssl_set_timer_cb_ctx( &ssl, &timer );
+            mbedtls_ssl_set_timer_cb_ctx( &ssl, &timer );
 #endif
-            }
 #endif /* MBEDTLS_TIMING_C */
 
             mbedtls_printf( " ok\n" );