nfsd: make NFSv4 lease time per net

Lease time is a part of NFSv4 state engine, which is constructed per network
namespace.

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 9047706..0c20be8 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -87,6 +87,8 @@
 
 	struct file *rec_file;
 	bool in_grace;
+
+	time_t nfsd4_lease;
 };
 
 extern int nfsd_net_id;