inotify: Work around the vput() bug directly

For 15.0, apply a minimal fix which at least ensures that inotify can't
trigger the latent race described in commit 99cb3dca4773 ("vnode: Rework
vput() to avoid holding the vnode lock after decrementing").

Approved by: re (cperciva)
Reviewed by: olce, kib
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D53774

(cherry picked from commit ebc17879f0885ca87644980f6275b9759b311eb3)
(cherry picked from commit 1f6e3abf41718e8e4a309be122f0a6048e9c5772)