nft: split parsing from netlink commands

nft: split parsing from netlink commands

This patch updates the parser to generate a list of command objects.
This list of commands is then transformed to a list of netlink jobs.
This new command object stores the rule using the nftnl representation
via nft_rule_new().

To reduce the number of updates in this patch, the nft_*_rule_find()
functions have been updated to restore the native representation to
skip the update of the rule comparison code.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Phil Sutter <phil@nwl.cc>