NDOF: fix helicopter fly option, revert default to trackball.

Rationale for using trackball is that it allows roll which you expect
with an ndof device.

source/blender/editors/interface/resources.c

@@ -2449,8 +2449,6 @@ void init_userdef_factory(void)
 	U.versions = 1;
 	U.savetime = 2;
 
-	U.ndof_flag |= NDOF_TURNTABLE;
-
 	{
 		Mesh *me;
 		for (me = G.main->mesh.first; me; me = me->id.next) {

source/blender/editors/space_view3d/view3d_edit.c

@@ -1333,6 +1333,10 @@ void view3d_ndof_fly(
 		mul_v3_fl(trans, speed * dt);
 		trans_orig_y = trans[1];
 
+		if (U.ndof_flag & NDOF_FLY_HELICOPTER) {
+			trans[1] = 0.0f;
+		}
+
 		/* transform motion from view to world coordinates */
 		mul_qt_v3(view_inv, trans);