fix for pas5211 exception

Change-Id: I8cafcdabe866923f25894e965da071337a63a4d4
diff --git a/voltha/adapters/microsemi/DeviceManager.py b/voltha/adapters/microsemi/DeviceManager.py
index 86e531e..960d13c 100644
--- a/voltha/adapters/microsemi/DeviceManager.py
+++ b/voltha/adapters/microsemi/DeviceManager.py
@@ -14,7 +14,6 @@
 # limitations under the License.
 #
 from uuid import uuid4
-from ofagent.utils import mac_str_to_tuple
 import structlog
 from voltha.protos.common_pb2 import ConnectStatus, OperStatus
 from voltha.protos.logical_device_pb2 import LogicalDevice, LogicalPort
@@ -23,6 +22,13 @@
 
 log = structlog.get_logger()
 
+def mac_str_to_tuple(mac):
+    """
+    Convert 'xx:xx:xx:xx:xx:xx' MAC address string to a tuple of integers.
+    Example: mac_str_to_tuple('00:01:02:03:04:05') == (0, 1, 2, 3, 4, 5)
+    """
+    return tuple(int(d, 16) for d in mac.split(':'))
+
 class DeviceManager(object):
 
     def __init__(self, device, adapter_agent):