kernel - allow PG_NOTMETA to be set on regular files too
* Allow this flag to be set for VM pages associated with regular files
too, the flag prevents the related VM page from being swapcache'd.
The flag is set by HAMMER on normal file buffer cache buffers when
double buffering is enabled to prevent swapcache from caching the
data twice.
* This also fixes an issue when a large number of files exceeding the
maxvnode limit are recycled, and double buffering is enabled along
with vm.swapcache.data_enable. We do not want swapcache to try to
cache the pages via the vnode, instead we'd rather it cache them
via the block device (whos vnode doesn't get recycled).