Update fallback policy for fast fallback.

[ Cherry-pick of http://ag/16064433 ]
[ Merge of http://go/wvgerrit/136329 ]

CDM core has been updated to support very short fallback durations in
the case of failures during OTA keybox provisioning.  This is intended
to be used during testing via specialized developer apps or GTS tests.

Bug: 187646550
Test: Android unit tests
Change-Id: I8a75d2e1c404d6caed535b087e8dd29da5c21b83

libwvdrmengine/cdm/core/include/okp_info.h

@@ -45,6 +45,7 @@ class SystemFallbackInfo {
     backoff_duration_ = (duration > 0 ? duration : 0);
   }
   void DoubleBackoffDuration() { backoff_duration_ *= 2; }
+  void ClearBackoffDuration() { backoff_duration_ = 0; }
 
   bool HasProvisioningTime() const { return provisioning_time_ != 0; }
   int64_t provisioning_time() const { return provisioning_time_; }