pyang: missing key in neutron port attribute
pyang: missing key in neutron port attribute

This patch fixes the following error by pyang.
ip version is missing for extra dhcp attribute and add key statement.

> neutron.yang:42: error: the list at "neutron.yang:42 (at neutron-ports.yang:54)" needs at least one key because it is used as config

Change-Id: Ie2ae3661799fc2b7179f028c4a586a1593e23c69
Signed-off-by: Isaku Yamahata <87b7f730b993ec3947ada6404f19ac98e56bb574@intel.com>

opendaylight/neutron