pcu: Enable 'egprs only' vty option if egprs requested

Change-Id: Idd0b5bf8769d693480268c0a0b89dbfd63779e48
diff --git a/src/osmo_gsm_tester/bts.py b/src/osmo_gsm_tester/bts.py
index 6b0331e..2ca44d2 100644
--- a/src/osmo_gsm_tester/bts.py
+++ b/src/osmo_gsm_tester/bts.py
@@ -131,6 +131,9 @@
     def remote_addr(self):
         return self.conf.get('addr')
 
+    def egprs_enabled(self):
+        return self.conf_for_bsc()['gprs_mode'] == 'egprs'
+
     def cleanup(self):
         'Nothing to do by default. Subclass can override if required.'
         pass