ms_osmo_mobile.py: Fix missing sublcass implementation of abstract MS methods

Change-Id: Icddab08c84ef97924d10801d7128158f515bcd01
diff --git a/src/osmo_gsm_tester/obj/ms_osmo_mobile.py b/src/osmo_gsm_tester/obj/ms_osmo_mobile.py
index f497772..cc54174 100644
--- a/src/osmo_gsm_tester/obj/ms_osmo_mobile.py
+++ b/src/osmo_gsm_tester/obj/ms_osmo_mobile.py
@@ -32,3 +32,9 @@
         if not ki:
             return "00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00"
         return ki
+
+    def get_assigned_addr(self, ipv6=False):
+        raise log.Error('API not implemented!')
+
+    def is_registered(self, mcc_mnc=None):
+        raise log.Error('API not implemented!')