Fix an invalid filter attribute when listing floating ips

Fix an invalid filter attribute when listing floating ips

The request doesn't conform with API [1] and raises exceptions vs
Neutron Hunter:

neutronclient.common.exceptions.BadRequest: [u'ip'] is invalid attribute for filtering
Neutron server returns request_ids: ['req-857b6294-eea5-46cf-8c95-0e57279ed5e6']

[1] https://developer.openstack.org/api-ref/network/v2/index.html?expanded=list-floating-ips-detail

Change-Id: I52bac8806152695834f8ece4f0213c3c63134c79
Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>