shm: do mlock/zeroing under shmem lock

fairmq/shmem/Manager.h

@@ -143,7 +143,6 @@ class Manager
             } catch(interprocess_exception& bie) {
                 LOG(error) << "something went wrong: " << bie.what();
             }
-        }
 
             if (mlockSegment) {
                 LOG(debug) << "Locking the managed segment memory pages...";
@@ -158,9 +157,6 @@ class Manager
                 LOG(debug) << "Successfully zeroed the managed segment free memory.";
             }
 
-        {
-            boost::interprocess::scoped_lock<boost::interprocess::named_mutex> lock(fShmMtx);
-
             fShmRegions = fManagementSegment.find_or_construct<Uint16RegionInfoHashMap>(unique_instance)(fShmVoidAlloc);
 
             fDeviceCounter = fManagementSegment.find<DeviceCounter>(unique_instance).first;