src: add set optimization options

src: add set optimization options

This patch adds options to choose set optimization mechanisms.

Two new statements are added to the set syntax, and they can be mixed:

 nft add set filter set1 { type ipv4_addr ; size 1024 ; }
 nft add set filter set1 { type ipv4_addr ; policy memory ; }
 nft add set filter set1 { type ipv4_addr ; policy performance ; }
 nft add set filter set1 { type ipv4_addr ; policy memory ; size 1024 ; }
 nft add set filter set1 { type ipv4_addr ; size 1024 ; policy memory ; }
 nft add set filter set1 { type ipv4_addr ; policy performance ; size 1024 ; }
 nft add set filter set1 { type ipv4_addr ; size 1024 ; policy performance ; }

Also valid for maps:

 nft add map filter map1 { type ipv4_addr : verdict ; policy performace ; }
 [...]

This is the output format, which can be imported later with `nft -f':

table filter {
	set set1 {
		type ipv4_addr
		policy memory
		size 1024
	}
}

In this approach the parser accepts default options such as 'performance',
given they are a valid configurations, but aren't sent to the kernel.

Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>