nft: Introduce nft-ruleparse.{c,h}

Extract all code dealing with parsing from struct nftnl_rule into struct
iptables_command_state from nft-shared.c into a separate source file.

Basically this is nft_rule_to_iptables_command_state() and the functions
it calls, plus family-independent parsers called from family-specific
callbacks.

Signed-off-by: Phil Sutter <phil@nwl.cc>
5 files changed