proc: Point /proc/mounts at /proc/thread-self/mounts instead of /proc/self/mounts

In oddball cases where the thread has a different mount namespace than
the thread group leader or more likely in cases where the thread
remains and the thread group leader has exited this ensures that
/proc/mounts continues to work.

This should not cause any problems but if it does this patch can just
be reverted.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

fs/proc/root.c

@@ -173,7 +173,7 @@ void __init proc_root_init(void)
 
 	proc_self_init();
 	proc_thread_self_init();
-	proc_symlink("mounts", NULL, "self/mounts");
+	proc_symlink("mounts", NULL, "thread-self/mounts");
 
 	proc_net_init();