tc: nat: ffs should operation on host byte ordered data

tc: nat: ffs should operation on host byte ordered data

In print_nat the mask length is calculated as

	len = ffs(sel->mask);
	len = len ? 33 - len : 0;

The mask is stored in network byte order, it should be converted
to host byte order before calculating first bit set.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>