Description of problem:
While syncing data from master to non-master zone, the non-master rgw process crashed with a Segfault.

Version-Release number of selected component (if applicable):
ceph-radosgw-10.2.2-15.el7cp.x86_64

Steps to Reproduce:
1. Configure rgw1 as master zone and upload around 300G of data to master zone.
2. Configure rgw2 as the second zone and start syncing data from rgw1. 
3. Add a delay of about 150ms between the two nodes.


Actual results:
Around 300G of data was uploaded on rgw1 before starting the sync and rgw2 had no data in it. Once the sync started, another 300G were added to rgw1. Process crashed on rgw2 after syncing 300G of data. 

2016-07-09 22:06:38.136383 7fdd437fe700 -1 *** Caught signal (Segmentation fault) **
 in thread 7fdd437fe700 thread_name:radosgw

 ceph version 10.2.2-15.el7cp (60cd52496ca02bdde9c2f4191e617f75166d87b6)
 1: (()+0x54e22a) [0x7fde5db4822a]
 2: (()+0xf100) [0x7fde5cf79100]
 3: (RGWCoroutinesStack::wakeup()+0xa) [0x7fde5d8c44aa]
 4: (RGWBucketShardFullSyncCR::operate()+0x8a1) [0x7fde5d971531]
 5: (RGWCoroutinesStack::operate(RGWCoroutinesEnv*)+0x7e) [0x7fde5d8c3a2e]
 6: (RGWCoroutinesManager::run(std::list<RGWCoroutinesStack*, std::allocator<RGWCoroutinesStack*> >&)+0x3f1) [0x7fde5d8c59d1]
 7: (RGWCoroutinesManager::run(RGWCoroutine*)+0x70) [0x7fde5d8c6590]
 8: (RGWRemoteDataLog::run_sync(int, rgw_data_sync_status&)+0x352) [0x7fde5d96d912]
 9: (RGWDataSyncProcessorThread::process()+0x49) [0x7fde5da30289]
 10: (RGWRadosThread::Worker::entry()+0x133) [0x7fde5d9d5083]
 11: (()+0x7dc5) [0x7fde5cf71dc5]
 12: (clone()+0x6d) [0x7fde5c57bced]