kill the awful check before mntinfo_add_list() in collect_mntns()

This check was added by commit aebfabb5 "mnt: add --ext-mount-map
auto option", but unless I am totally confused it actually belongs
to the (already reverted) 246367e4 "add walk_all flag to
walk_namespaces".

Remove it. It is no longer needed and it was very unobvious.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Tested-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

mount.c

@@ -2674,8 +2674,7 @@ static int collect_mntns(struct ns_id *ns, void *__arg)
 	if (arg->for_dump && ns->pid != getpid())
 		arg->need_to_validate = true;
 
-	if (ns->pid != getpid() || !(root_ns_mask & CLONE_NEWNS))
-		mntinfo_add_list(pms);
+	mntinfo_add_list(pms);
 	return 0;
 }