owners.yaml: add the tuntap subsystem

tuntap driver is currently not listed in owners.yaml, this may falsely
lead to the conclusion it is not maintained. Actually, Jason has been
taking care of it from some time now.

Let's make this explicit, adding a tuntap subsystem, listing Jason as
the maintainer and ensuring this is properly tested using lnst.

Signed-off-by: Andrea Claudi aclaudi@redhat.com