Enable ovn_emit_need_to_frag

Enabled by default since this branch only supports jammy where the
kernel and ovn are new enough to support this flag. This will eliminate
the need for a more complex change or the use of a dedicated opt-in
config option.

For more details, please refer to
I089f95b40803a6cd5e01990acacd599ced3bbd91

Closes-Bug: #1947391
Change-Id: Icc05980b4bc9184ba4e52722c6c11abfcfc0d58c

src/reactive/neutron_api_plugin_ovn_handlers.py

@@ -98,6 +98,11 @@ def configure_neutron():
                 ('ovn_dhcp6_global_options',
                     ','.join(
                         _split_if_str(options.ovn_dhcp6_global_options))),
+                # Only safe on Ubuntu releases which have a kernel
+                # version of 5.2 or greater.  Enabled by default
+                # because charm supports focal or newer which has a
+                # minimum kernel version of 5.4.
+                ('ovn_emit_need_to_frag', True),
                 # NOTE(fnordahl): will be used on chassis with DPDK enabled
                 #
                 # Neutron will make per chassis decisions based on chassis

unit_tests/test_reactive_neutron_api_plugin_ovn_handlers.py

@@ -158,6 +158,7 @@ class TestOvnHandlers(test_utils.PatchHelper):
                                 ('dhcp_default_lease_time', 42),
                                 ('ovn_dhcp4_global_options', 'a:A4,b:B4'),
                                 ('ovn_dhcp6_global_options', 'a:A6,b:B6'),
+                                ('ovn_emit_need_to_frag', True),
                                 ('vhost_sock_dir', '/run/libvirt-vhost-user')
                             ],
                             'ml2_type_geneve': [