Modify the maximum length of subnets contain the same EndpointID
Modify the maximum length of subnets contain the same EndpointID

This patch modifes _get_subnets_by_attrs to examine the new maximum
length, 2 for IPv4 and IPv6 each other, for the subnets that have the
same EndpointID.

Change-Id: I16fb57bfebde19b51fac184c6615b90d568c3bf4
Signed-off-by: Taku Fukushima <d385cb54d860d8a5dcc6157b54cf213091772451@gmail.com>
Closes-Bug: #1503973

celebdor/kuryr,midonet/kuryr,celebdor/kuryr,midonet/kuryr,celebdor/kuryr-libnetwork,celebdor/kuryr-libnetwork,openstack/kuryr,openstack/kuryr,midonet/kuryr,celebdor/kuryr-libnetwork