The flag is trivially avoidable and its removal will facilitate further cleanup of the vn_start_write API
```
commit e03e8e9a6ab5ac0e2c5e3d7f0ae693ace60d5da3
Author: Mateusz Guzik <mjg@FreeBSD.org>
Date: Sat Sep 10 22:13:19 2022 +0200
vfs: retire the V_MNTREF flag
Reviewed by:
Differential Revision:
commit ea71ac5e72da4a343bd9f5e72ab0ace18e0d19ed
Author: Mateusz Guzik <mjg@FreeBSD.org>
Date: Sat Sep 10 22:12:08 2022 +0200
vfs: stop using the V_MNTREF flag
Reviewed by:
Differential Revision:
commit 49e1ef36ff3d5731dbb4b6f20f39ed7b838ac543
Author: Mateusz Guzik <mjg@FreeBSD.org>
Date: Sat Sep 10 22:11:42 2022 +0200
ufs: stop using the V_MNTREF flag
Reviewed by:
Differential Revision:
```