I suggest patching Trusty to remove the lock file on boot, before ebtables has any chance to run, if that's possible. That seems to me to be the minimal fix that would resolve any user impact on Trusty. Using /run is a better way to do that, and in the future we'll do it that way (since Zesty has this fixed) but for a stable release update we prefer the minimal and least disruptive fix over a "correct" one.
I suggest patching Trusty to remove the lock file on boot, before ebtables has any chance to run, if that's possible. That seems to me to be the minimal fix that would resolve any user impact on Trusty. Using /run is a better way to do that, and in the future we'll do it that way (since Zesty has this fixed) but for a stable release update we prefer the minimal and least disruptive fix over a "correct" one.