ovn: Gratuitous ARP for centralized NAT rules on a distributed router

ovn: Gratuitous ARP for centralized NAT rules on a distributed router

This patch extends gratuitous ARP support for NAT addresses so that it
applies to centralized NAT rules on a distributed router, in addition to
the existing gratuitous ARP support for NAT addresses on gateway routers.
Centralized NAT rules have type other than "dnat_and_snat", or have type
"dnat_and_snat" but do not specify external_mac or logical_port.  These
NAT rules apply on the redirect-chassis.

Gratuitous ARP packets for centralized NAT rules on a distributed router
are only generated on the redirect-chassis.  This is achieved by extending
the syntax for "options:nat-addresses" in the southbound database,
allowing the condition 'is_chassis_resident("LPORT_NAME")' to be appended
after the MAC and IP addresses.  This condition is automatically inserted
by ovn-northd when the northbound "options:nat-addresses" is set to
"router" and the peer is a distributed gateway port.

A separate patch will be required to support gratuitous ARP for
distributed NAT rules that specify logical_port and external_mac.  Since
the MAC address differs and the logical port often resides on a different
chassis from the redirect-chassis, these addresses cannot be included in
the same "nat-addresses" string as for centralized NAT rules.

Signed-off-by: Mickey Spiegel <mickeys.dev@gmail.com>
Signed-off-by: Gurucharan Shetty <guru@ovn.org>