The former MTU (1450) is fine for VXLAN but reducing it to 1442
allows GENEVE tunneled networks.
Else snaps_smoke fails when verifying OVN [1].
[1] https://artifacts.opnfv.org/logs/functest/lf-pod1/gambia/2018-11-05_11-43-15/functest.log
Change-Id: Icf38c30837858f59ed25f443245fee0007e9354d
Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>
             self.pub_net_config = openstack_tests.get_pub_net_config(
                 project_name=self.os_creds.project_name,
                 net_name=guid + '-pub-net',
-                mtu=1450, subnet_name=guid + '-pub-subnet',
+                mtu=1442, subnet_name=guid + '-pub-subnet',
                 router_name=guid + '-pub-router',
                 external_net=self.ext_net_name)