tunnel: add geneve support

tunnel: add geneve support

This patch extends the tunnel metadata object to define geneve tunnel
specific configurations:

table netdev x {
	tunnel y {
		id 10
		ip saddr 192.168.2.10
		ip daddr 192.168.2.11
		sport 10
		dport 20
		ttl 10
		geneve {
			class 0x1010 opt-type 0x1 data "0x12345678"
			class 0x1020 opt-type 0x2 data "0x87654321"
			class 0x2020 opt-type 0x3 data "0x87654321abcdeffe"
		}
	}
}

Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>