NFSd: make boot_time variable per network namespace

NFSd's boot_time represents grace period start point in time.

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 b6deebd..65c2431 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -37,6 +37,7 @@
 
 	struct lock_manager nfsd4_manager;
 	bool grace_ended;
+	time_t boot_time;
 };
 
 extern int nfsd_net_id;