selftests: forwarding: lib.sh: Add wait for dev with timeout

Add a function that waits for device with maximum number of iterations.
It enables to limit the waiting and prevent infinite loop.

This will be used by the subsequent patch which will set two ports to
different speeds in order to make sure they cannot negotiate a link.

Waiting for all the setup is limited with 10 minutes for each device.

Signed-off-by: Amit Cohen <amitc@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>