nfsd: filecache: use list_lru_walk_node() in nfsd_file_gc()

nfsd: filecache: use list_lru_walk_node() in nfsd_file_gc()

list_lru_walk() is only useful when the aim is to remove all elements
from the list_lru.  It will repeatedly visit rotated elements of the
first per-node sublist before proceeding to subsequent sublists.

This patch changes nfsd_file_gc() to use list_lru_walk_node() and
list_lru_count_node() on each NUMA node.

Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>