tools: ynl: add sample for devlink

Add a sample to show off how to issue basic devlink requests.
For added testing issue get requests while walking a dump.

$ ./devlink
netdevsim/netdevsim1:
    driver: netdevsim
    running fw:
        fw.mgmt: 10.20.30
    ...
netdevsim/netdevsim2:
    driver: netdevsim
    running fw:
        fw.mgmt: 10.20.30
    ...

Signed-off-by: Jakub Kicinski <kuba@kernel.org>