nfsd: make export cache allocated per network namespace context

This patch also changes prototypes of nfsd_export_flush() and exp_rootfh():
network namespace parameter added.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 12e0cff..c1c6242 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -28,6 +28,8 @@
 
 struct nfsd_net {
 	struct cld_net *cld_net;
+
+	struct cache_detail *svc_export_cache;
 };
 
 extern int nfsd_net_id;