net: Fix delay in net_retry test

Introduced in 45b47734 (net/arp: account for ARP delay, avoid duplicate packets on timeout)

Check the arp timeout and adjust the timeout start time before the call
to eth_recv() so that the sandbox driver has the opportunity to adjust
the sandbox timer after the new start time has been recorded.

Also, change the adjustment amount by 11 seconds instead of exactly the
10 seconds that the ping timout is expecting since the timeout check is
looking for the time elapsed to be greater than but not equal to the
specified delay.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Acked-by: Simon Glass <sjg@chromium.org>