inotify: Fix a couple of locking bugs

[markj]

Summary

When hooking vop_rename_post(), the preexisting dst vnode will be
unlocked. But, we need to invoke VOP_GETATTR on it in vn_inotify() to
check its link count.

In inotify_unlink_watch_locked(), the vnode interlock is not held, so
don't use vn_irflag_unset_locked().

Fixes: f1f230439fa4 ("vfs: Initial revision of inotify")

[kib]

sys/sys/inotify.h

110

_[A_Z]* are not good names for global macros.
I suggest e.g. INOTIFY_NAME_LOCK() or similar.

117

Same as () are not needed in around vp/dvp in lines 111/112.

[markj]

Handle kib's notes.