ms: Fix and use ms msisdn() getter

The getter method was named the same as the itnernal field, and hence
when used it would fail since the intenral field would be sleect and
fail to be called.

Change-Id: I2f631eb6256eb0e065f41d5b7531395c4a054cd8
diff --git a/sysmocom/suites/nitb_smpp/esme_ms_sms_storeforward.py b/sysmocom/suites/nitb_smpp/esme_ms_sms_storeforward.py
index f9617e2..f4d379c 100755
--- a/sysmocom/suites/nitb_smpp/esme_ms_sms_storeforward.py
+++ b/sysmocom/suites/nitb_smpp/esme_ms_sms_storeforward.py
@@ -27,13 +27,13 @@
 esme.connect()
 nitb.subscriber_add(ms)
 
-wrong_msisdn = ms.msisdn + esme.msisdn
+wrong_msisdn = ms.msisdn() + esme.msisdn
 print('sending sms with wrong msisdn %s, it will fail' % wrong_msisdn)
 msg = Sms(esme.msisdn, wrong_msisdn, 'smpp message with wrong dest')
 esme.run_method_expect_failure(SMPP_ESME_RINVDSTADR, esme.sms_send_wait_resp, msg, esme.MSGMODE_STOREFORWARD)
 
 print('sending sms, it will be stored...')
-msg = Sms(esme.msisdn, ms.msisdn, 'smpp send not-yet-registered message')
+msg = Sms(esme.msisdn, ms.msisdn(), 'smpp send not-yet-registered message')
 umref = esme.sms_send_wait_resp(msg, esme.MSGMODE_STOREFORWARD, receipt=True)
 
 print('MS registers and will receive the SMS...')
@@ -45,7 +45,7 @@
 wait(esme.receipt_was_received, umref)
 
 print('checking MS can receive SMS while registered...')
-msg = Sms(esme.msisdn, ms.msisdn, 'smpp send already-registered message')
+msg = Sms(esme.msisdn, ms.msisdn(), 'smpp send already-registered message')
 umref = esme.sms_send_wait_resp(msg, esme.MSGMODE_STOREFORWARD, receipt=True)
 wait(ms.sms_was_received, msg)
 print('Waiting to receive and consume sms receipt with reference', umref)