Update to kind-0.11.1. Override mtu manually.

Created by: garloff

This is my attempt to update to latest kind (0.11.1 currently). The old way to set mtu to 1400 does not work any more. We just patch the dockerd startup script (systemd file) and manually set it. Things appear to work.

Signed-off-by: Kurt Garloff scs@garloff.de