[U-Boot] Driver model test breakages

[Joe Hershberger]

>> 45b47734     net/arp: account for ARP delay, avoid duplicate packets on timeout
>
> This is still broken - Joe do you have any ideas? The release is coming soonish.

This was the first commit that caused the timeout to not get skipped,
however it would time out and proceed.

What caused the test to start hanging indefinitely is this commit:

159fb22 (sandbox: add a sandbox timer and basic test)

I'm still looking into why.

-Joe