netfilter: xt_helper: Use sizeof(variable) instead of literal number

It's better to use sizeof(info->name)-1 as index to force set the string
tail instead of literal number '29'.

Signed-off-by: Gao Feng <fgao@ikuai8.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
1 file changed