netdevsim: shared UDP tunnel port table support

Add the ability to simulate a device with a shared UDP tunnel port
table.

Try to reject the configurations and actions which are not supported
by the core, so we don't get syzcaller etc. warning reports.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>