Bug-1409: Fix empty Update message (EOR) handling.

-Processing of EOR in BGPSynchronization#updReceived ends up with NPE
-fixed behaviour - synchronize Ipv4 Unicast

Change-Id: I6b85cbcfd8ff9ec00c99b9f11b4bb2dce75ef334
Signed-off-by: Milos Fabian <milfabia@cisco.com>