CI: RFsim tests: Wait for IP

Ensure that the UE has an IP address before continuing the test.
Otherwise, it might happen we ping before the UE is connected.

Do not do this in do-ra and phytest, as they use --noS1, which implies
statically assigned IP address, so IP address check always succeeds(!).

ci-scripts/xml_files/container_5g_f1_rfsim.xml

@@ -29,6 +29,7 @@
  100021
  000021
  000022
+ 000023
  020021
  030021
  030022
@@ -59,6 +60,12 @@
                 <nb_healthy>8</nb_healthy>
         </testCase>
 
+        <testCase id="000023">
+                <class>Attach_UE</class>
+                <desc>Attach OAI UE (Wait for IP)</desc>
+                <id>rfsim5g_ue</id>
+        </testCase>
+
         <testCase id="020021">
                 <class>Ping</class>
                 <desc>Ping ext-dn from all NR-UEs</desc>