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/smpp/esme_ms_sms_transaction.py b/sysmocom/suites/smpp/esme_ms_sms_transaction.py
index 5a5a470..5efaf66 100755
--- a/sysmocom/suites/smpp/esme_ms_sms_transaction.py
+++ b/sysmocom/suites/smpp/esme_ms_sms_transaction.py
@@ -42,16 +42,16 @@
 wait(msc.subscriber_attached, ms)
 
 print('sending first sms...')
-msg = Sms(esme.msisdn, ms.msisdn, 'smpp send message')
+msg = Sms(esme.msisdn, ms.msisdn(), 'smpp send message')
 esme.sms_send(msg, esme.MSGMODE_TRANSACTION)
 wait(ms.sms_was_received, msg)
 
 print('sending second sms (unicode chars not in gsm aplhabet)...')
-msg = Sms(esme.msisdn, ms.msisdn, 'chars:[кизаçйж]')
+msg = Sms(esme.msisdn, ms.msisdn(), 'chars:[кизаçйж]')
 esme.sms_send(msg, esme.MSGMODE_TRANSACTION)
 wait(ms.sms_was_received, msg)
 
-wrong_msisdn = ms.msisdn + esme.msisdn
+wrong_msisdn = ms.msisdn() + esme.msisdn
 print('sending third sms (with wrong msisdn %s)' % 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_TRANSACTION)