nfsd: make expkey cache allocated per network namespace context

This patch also changes svcauth_unix_purge() function: added network namespace
as a parameter and thus loop over all networks was replaced by only one call
for ip map cache purge.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index ddb9f87..b144177 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -129,13 +129,14 @@
 {
 	int err;
 	struct seq_file *seq;
+	struct nfsd_net *nn = net_generic(&init_net, nfsd_net_id);
 
 	err = seq_open(file, &nfs_exports_op);
 	if (err)
 		return err;
 
 	seq = file->private_data;
-	seq->private = &svc_export_cache;
+	seq->private = nn->svc_export_cache;
 	return 0;
 }