modemmanager: Add a reason to ConnectionStateChanged events.

This can be used by a connection manager to decide to respond in a different way
to certain kinds of disconnects (e.g. intentional versus unintentional versus
suspension).

TEST=None
This change introduces no additional code, so testing it in isolation is not
possible.

BUG=chromium-os:6744

Change-Id: Ie371e20ec7a003333eba013af3ad61c0e494a4ad
Signed-Off-By: Elly Jones <ellyjones@chromium.org>

Review URL: http://codereview.chromium.org/3413011
(cherry picked from commit 29a9674b818fd64c19bad84f526f6fa68edec174)

introspection/org.freedesktop.ModemManager.Modem.xml

@@ -93,6 +93,11 @@
           Reason for state transition.
         </tp:docstring>
       </arg>
+      <arg name="reason" type="u" tp:type="MM_MODEM_CONNECTION_STATE_CHANGED_REASON">
+        <tp:docstring>
+          Reason for this state change.
+        </tp:docstring>
+      </arg>
     </signal>
 
     <property name="Device" type="s" access="read">
@@ -211,5 +216,24 @@
       </tp:enumvalue>
     </tp:enum>
 
+    <tp:enum name="MM_MODEM_CONNECTION_STATE_CHANGE_REASON" type="u">
+      <tp:enumvalue suffix="UNKNOWN" value="0">
+        <tp:docstring>
+          Reason unknown or not reportable.
+        </tp:docstring>
+      </tp:enumvalue>
+      <tp:enumvalue suffix="REQUESTED" value="1">
+        <tp:docstring>
+          Connection state change was requested by an interface user.
+        </tp:docstring>
+      </tp:enumvalue>
+      <tp:enumvalue suffix="SUSPEND" value="2">
+        <tp:docstring>
+          Connection state change was caused by a system suspend.
+        </tp:docstring>
+      </tp:enumvalue>
+    </tp:enum>
+
+
   </interface>
 </node>