Rehome DHCP_IPV{4,6}_TABLE constants to neutron-lib

2 new constants DHCP_IPV4_TABLE and DHCP_IPV6_TABLE were added to
the openvswitch agent's constant module in [1].
As whole this constants module is now rehomed to the neutron_lib,
this patch also rehomes that 2 new constants.

[1] https://review.opendev.org/c/openstack/neutron/+/776567

Change-Id: I242a3191e7481c0b75a5785db23dcc031d74140a

neutron_lib/constants.py

@@ -722,6 +722,10 @@ TRANSIENT_TABLE = 60
 LOCAL_MAC_DIRECT = 61
 TRANSIENT_EGRESS_TABLE = 62
 
+# Table for DHCP
+DHCP_IPV4_TABLE = 77
+DHCP_IPV6_TABLE = 78
+
 # Tables used for ovs firewall
 BASE_EGRESS_TABLE = 71
 RULES_EGRESS_TABLE = 72
@@ -756,6 +760,8 @@ INT_BR_ALL_TABLES = (
     BASE_EGRESS_TABLE,
     RULES_EGRESS_TABLE,
     ACCEPT_OR_INGRESS_TABLE,
+    DHCP_IPV4_TABLE,
+    DHCP_IPV6_TABLE,
     BASE_INGRESS_TABLE,
     RULES_INGRESS_TABLE,
     ACCEPTED_EGRESS_TRAFFIC_TABLE,

releasenotes/notes/rehome-dhcp-table-constants-779598680f803e2a.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    ``DHCP_IPV4_TABLE`` and ``DHCP_IPV6_TABLE`` constants from the
+    ``neutron.plugins.ml2.drivers.openvswitch.agent.common.constants`` module
+    are now available in ``neutron_lib.constants``.