vfs cache: Add NAMEILOOKUP to the whitelist of fastpath lookup flags

Otherwise the lockless name lookup path is inadvertently disabled since
NAMEILOOKUP isn't recognized.

Reviewed by: olce, kib
Fixes: 7587f6d4840f ("namei: Make stackable filesystems check harder for jail roots")
Differential Revision: https://reviews.freebsd.org/D50532

(cherry picked from commit f4158953007f557061d91f99d2374d48d8376cc6)