It's in the normal Ubuntu repositories for xenial. Assuming that you haven't explicitly disabled them, You should be able to run "sudo apt-get update" followed by "sudo apt-get install linux-image-4.4.0-38-generic" to reinstall the beastie.
It's in the normal Ubuntu repositories for xenial. Assuming that you haven't explicitly disabled them, You should be able to run "sudo apt-get update" followed by "sudo apt-get install linux-image- 4.4.0-38- generic" to reinstall the beastie.