parser: support of maps with timeout

parser: support of maps with timeout

Support of key and value association with a certain timeout.

Example:

nft add map nftlb mapa { type inet_service: ipv4_addr\;
 timeout 5s\; }

Results in:

table ip nftlb {
	map mapa {
		type inet_service : ipv4_addr
		timeout 5s
	}
}

Signed-off-by: Laura Garcia Liebana <nevola@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>