mxmount: Use /usr/local/system/perl/bin/perl

We might transfer /usr/bin/perl to a /pkg package in the future as we
did with python. mxmount needs to be able to run before the automounter
is available. Update perl path to /usr/local/system/perl/bin/perl, which
is always available.

mxmount/mxmount

@@ -1,4 +1,4 @@
-#!/usr/bin/perl
+#! /usr/local/system/perl/bin/perl
 
 use strict;
 use warnings;