[PATCH] brctl: add support for showstp command

[Denys Vlasenko]

Applied with some changes, please try current git.

> +       read_leaf(name, "brport", "hairpin_mode");
> +       if (!LONE_CHAR(filedata, '0'))
> +               printf("\n hairpin mode\t\t\%4u", xstrtou(filedata, 0));

Should be
    "\n hairpin mode\t\t%4u"
not
    "\n hairpin mode\t\t\%4u"
right?