Fix default for DeviceAutoUpdateP2PEnabled

The default for DeviceAutoUpdateP2PEnabled has never been right (See
crbug.com/256569100). Update it to the actual value, we are unlikely to
change the implementation at this point.

The wrong default value makes our server-side UI display unexpected
values to customers. While it can be worked around, it confuses
everyone.

Bug: 256569100, 384818295
Change-Id: Ic73138f09d33664ff1b39b66ab4e085db45b9d21
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6734614
Auto-Submit: Victor Gabriel Savu <vsavu@google.com>
Commit-Queue: Victor Gabriel Savu <vsavu@google.com>
Reviewed-by: Sergey Poromov <poromov@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1487414}