sub sort_by_intf # sort interface alpha/number name mixture properly
{ my $A = $a;    # just turn any number into a 0004 digit one
  my $B = $b;
  $A =~ s/([0-9]+)/ sprintf "%04d",9999-$1 /ge;
  $B =~ s/([0-9]+)/ sprintf "%04d",9999-$1 /ge;
  $B cmp $A; # reverse order happens to be useful here:
}            # Tun0, Ser1, Port-channel2, Gi3, Fa4, Eth5