Merge "Use directly neutron.common.constants constants in l3_dvr_db"

diff --cc neutron/db/l3_dvr_db.py
Simple merge

diff --cc neutron/tests/functional/services/l3_router/test_l3_dvr_router_plugin.py
Simple merge

diff --cc neutron/tests/unit/db/test_l3_dvr_db.py
Simple merge