Also use DevicePolicy::GetAuP2PEnabled() to determine if p2p is enabled

With this change update_engine will use p2p either if the user has
manually enabled it (through the crosh flag) OR if the enterprise has
enabled it in Enterprise Policy.

BUG=chromium:260442
TEST=New unit tests + unit tests pass.

Change-Id: I54cd92c481bd2fd7c90232d7137ce2b37fa2ce61
Reviewed-on: https://chromium-review.googlesource.com/168950
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: David Zeuthen <zeuthen@chromium.org>
Tested-by: David Zeuthen <zeuthen@chromium.org>
diff --git a/update_attempter.cc b/update_attempter.cc
index ea1c619..ae9be74 100644
--- a/update_attempter.cc
+++ b/update_attempter.cc
@@ -217,6 +217,7 @@
     LOG(INFO) << "No device policies/settings present.";
 
   system_state_->set_device_policy(device_policy);
+  system_state_->p2p_manager()->SetDevicePolicy(device_policy);
 }
 
 void UpdateAttempter::CalculateP2PParams(bool interactive) {