ms_srs: refactor UE state getter functions

rename UE helper functions to query RRC connected/idle state
and adapt tests accordingly

also add helper to retrieve assinged IP address

Change-Id: I6cd057e34b4df6a1a73695355dd6406d7e039546
diff --git a/sysmocom/suites/4g/iperf3_ul.py b/sysmocom/suites/4g/iperf3_ul.py
index 453cdfa..6e24070 100755
--- a/sysmocom/suites/4g/iperf3_ul.py
+++ b/sysmocom/suites/4g/iperf3_ul.py
@@ -26,7 +26,7 @@
 proc = iperf3cli.prepare_test_proc(iperf3cli.DIR_UL, ue.netns(), bitrate=max_rate)
 
 print('waiting for UE to attach...')
-wait(ue.is_connected, None)
+wait(ue.is_rrc_connected)
 print('UE is attached')
 
 print("Running iperf3 client to %s through %s" % (str(iperf3cli), ue.netns()))