Attempts are spaced out with exponential backoff, cut at 10 minutes per
attempt.
Also avoid trying to acquire an IP on interfaces that aren't up.
Fixes#6126.
Fixes#6125.
The current parsing code assumed the ascii lowercase letters came after
the ascii numbers, which is not the case, and as such corrupted any mac
address that included hex letters (a-f). We likely did not notice this
as QEMU's emulated MAC is made up of only hex digits.
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
