Prevent adding a new CDMA call if know it will fail.

See code change for additional comments.

The same CDMA command is used for merging two calls, swapping between
two calls, and adding a new call on CDMA devices. The actual function of
the command depends on the context. Instead of issuing an 'add-call'
when we know the function will do something different given the
context, send back a more meaningful error.

Bug: 22850789
Change-Id: I45b51b15f3ef2f144411db5df86536704bd1201d
diff --git a/res/values/strings.xml b/res/values/strings.xml
index 1f65c3d..4f7cd53 100644
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -1315,4 +1315,9 @@
         A SIM card has activated your service and updated your phone\'s roaming capabilities.
     </string>
 
+    <!-- Call failure reason: Cannot add a call because there are already too many active calls. -->
+    <string name="callFailed_cdma_call_limit">
+        There are too many active calls. Please end or merge existing calls before placing a new one.
+    </string>
+
 </resources>