rework automatic creation of built-in table and chains

rework automatic creation of built-in table and chains

This patch reworks the automatic creation of built-in table and
chains. Now it initializes all built-in chains belonging a table
at once.

This happens with commands: -P, -A, -I, -N

Note that xtables skips chain initialization if it notices that
the table already exists in the kernel.

Thanks to Tomasz Bursztyka for spotting problems with -N.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>