VOP_FSYNC(): always require the locked vnode

[kib]

Summary

g_vfs_close_unlocked(9): wrapper around g_vfs_close(9)

that locks both bo vnode and topology.


filesystems: use g_vfs_close_unlocked(9)

As result, we lock the devvp vnode around calls to VOP_FSYNC() on
unmount. For instance, the vn_fsync_buf() implementation of fsync()
needs exclusive lock on the vnode to guarantee that all dirty buffers
are indeed synced.


VFS: require locked vnode for fsync()

Stop exempting devfs nodes.

Tested by:      pho