patch 8.0.0877: using CTRL-\ CTRL-N in terminal is inconsistent

Problem:    Using CTRL-\ CTRL-N in terminal is inconsistent.
Solution:   Stay in Normal mode.
diff --git a/src/option.c b/src/option.c
index d937d02..3b2949c 100644
--- a/src/option.c
+++ b/src/option.c
@@ -8228,7 +8228,7 @@
     {
 # ifdef FEAT_TERMINAL
 	/* Cannot set 'modifiable' when in Terminal mode. */
-	if (term_in_terminal_mode()
+	if (term_in_normal_mode()
 			 || (bt_terminal(curbuf) && !term_is_finished(curbuf)))
 	{
 	    curbuf->b_p_ma = FALSE;