kernel/vfs: enable accounting for ro mounts
* Some filesystems may be first mounted read-only and then upgraded
to read-write status
* The VFS layer has no provision for signaling VFSes of status change,
mount-point specific initialization code can only be run for the
initial mount
* VFS accounting was thus never enabled on a ro->rw mount point transition
* Bite the bullet and run vq_init() unconditionally for both read-only
and read-write mounts, the cost is only a few variables set to NULL
or zero anyway.