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_rfsim_24prb.xml

@@ -30,6 +30,7 @@
  100001
  000001
  000002
+ 000003
  020001
  020002
  030001
@@ -61,6 +62,12 @@
                 <nb_healthy>7</nb_healthy>
         </testCase>
 
+        <testCase id="000003">
+                <class>Attach_UE</class>
+                <desc>Attach OAI UE (Wait for IP)</desc>
+                <id>rfsim5g_ue</id>
+        </testCase>
+
         <testCase id="020001">
                 <class>Ping</class>
                 <desc>Ping ext-dn from NR-UE</desc>