iptables: Get rid of the iterator macro

iptables: Get rid of the iterator macro

Instead implement the iterator loop directly. Since both dump_entry()
and add_entry() have calculated 'builtin' and 'offset' let's pass in
them in as well.

In the next step we are able to remove also the table argument
which will allow us to unify the parsing the table we get
from IPT_SO_GET_ENTRIES and the table we will pass in to the kernel
via IPT_SO_SET_REPLACE.