I've re-tested with the proposed changes upstream; MTU is correctly set to 65000 for all tunnel types including GRE on 4.4 kernels; the kernel fix for bug 1743746 is required for support on >= Artful or if the HWE edge kernel is in use on Xenial.
I've re-tested with the proposed changes upstream; MTU is correctly set to 65000 for all tunnel types including GRE on 4.4 kernels; the kernel fix for bug 1743746 is required for support on >= Artful or if the HWE edge kernel is in use on Xenial.