server: unmask ObjectManager signals

This slipped by after pyphosphor changed the startup mask state
for signals in the ObjectManager/Properties bindings.

Change-Id: I16ff8bb4dc348c158abdbde4671886565e3ad309
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/obmc/mapper/server.py b/obmc/mapper/server.py
index 18edf55..4e9289c 100644
--- a/obmc/mapper/server.py
+++ b/obmc/mapper/server.py
@@ -275,6 +275,7 @@
         print "ObjectMapper discovery complete"
         self.service = dbus.service.BusName(
             obmc.mapper.MAPPER_NAME, self.bus)
+        self.manager.unmask_signals()
         return False
 
     def discovery_callback(self, owner, items):