make proc_ns_operations work with struct ns_common * instead of void *

We can do that now.  And kill ->inum(), while we are at it - all instances
are identical.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/namespace.c b/fs/namespace.c
index 5c21fda..b9c16c3 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3149,7 +3149,7 @@
 	return visible;
 }
 
-static void *mntns_get(struct task_struct *task)
+static struct ns_common *mntns_get(struct task_struct *task)
 {
 	struct ns_common *ns = NULL;
 	struct nsproxy *nsproxy;
@@ -3165,12 +3165,12 @@
 	return ns;
 }
 
-static void mntns_put(void *ns)
+static void mntns_put(struct ns_common *ns)
 {
 	put_mnt_ns(to_mnt_ns(ns));
 }
 
-static int mntns_install(struct nsproxy *nsproxy, void *ns)
+static int mntns_install(struct nsproxy *nsproxy, struct ns_common *ns)
 {
 	struct fs_struct *fs = current->fs;
 	struct mnt_namespace *mnt_ns = to_mnt_ns(ns);
@@ -3203,17 +3203,10 @@
 	return 0;
 }
 
-static unsigned int mntns_inum(void *ns)
-{
-	struct ns_common *p = ns;
-	return p->inum;
-}
-
 const struct proc_ns_operations mntns_operations = {
 	.name		= "mnt",
 	.type		= CLONE_NEWNS,
 	.get		= mntns_get,
 	.put		= mntns_put,
 	.install	= mntns_install,
-	.inum		= mntns_inum,
 };