vfs: fixup WANTIOCTLCAPS on open
In some cases vn_open_cred overwrites cn_flags, effectively nullifying
initialisation done in NDINIT. This will have to be fixed.
In the meantime make sure the flag is passed.
Reported by: jenkins
Noted by: Mathieu <sigsys@gmail.com>
(cherry picked from commit b7262756e2f471f6481070e2473af7853506b150)