The `octavia_provider_network_mtu-parameter` defaults to 1500
to not accidentially use `global_physnet_mtu` on deployment with
large MTU settings
Change-Id: I9fa33c5ee76197191f1e66b7a70a4c1c0a5fa394
(cherry picked from commit 2f1a3b4db1664cd9492bd32d1bad1793d5e61368)