NSX|V3: Fix ipam to check subnets carefully

IPAM supports several types of subnets, and not all with the same attributes.
_is_supported_net should check if the subnet has a cidr before checking it, as
'any' subnet does not.

Change-Id: I7f567daf247233843b59ab932256e752ce62c309

vmware_nsx/services/ipam/nsx_v3/driver.py

@@ -59,6 +59,8 @@ class Nsxv3IpamDriver(common.NsxAbstractIpamDriver):
 
     def _is_supported_net(self, subnet_request):
         """This driver doesn't support multicast cidrs"""
+        if not hasattr(subnet_request, "subnet_cidr"):
+            return True
         net = netaddr.IPNetwork(subnet_request.subnet_cidr[0])
         return not net.is_multicast()