`tap` has its default value set to `None`, but in the openapi yaml file
we've been setting it to `""`.
When using this code on the Kata Containers side we'd be hit by a non
expected behaviour of cloud-hypervisor, as even when using a different
method to initialise the `tuntap` device the code would be treated as if
using `--net tap` (which is a valid use-case).
Related: #3554
Signed-off-by: Fabiano Fidêncio <fabiano.fidencio@intel.com>
cb15ae5462