supplicant(interface): Add an event for bssid changes

This is useful in debugging (& collecting metrics) when the active bssid changes.

Bug: 36451639
Test: Compiles & manual tests using the framework changes.
Change-Id: I5676dfb9ec9c13ae900c315eb8dfacb857e70fc1
diff --git a/wifi/supplicant/1.0/ISupplicantStaIfaceCallback.hal b/wifi/supplicant/1.0/ISupplicantStaIfaceCallback.hal
index 166ad96..173cce9 100644
--- a/wifi/supplicant/1.0/ISupplicantStaIfaceCallback.hal
+++ b/wifi/supplicant/1.0/ISupplicantStaIfaceCallback.hal
@@ -346,6 +346,24 @@
   };
 
   /**
+   * BSSID change Reasons.
+   */
+  enum BssidChangeReason : uint8_t {
+    /**
+     * Started association with new bssid.
+     */
+    ASSOC_START = 0,
+    /**
+     * Completed association with new bssid.
+     */
+    ASSOC_COMPLETE = 1,
+    /**
+     * Dis-association with current bssid.
+     */
+    DISASSOC = 2
+  };
+
+  /**
    * Used to indicate that a new network has been added.
    *
    * @param id Network ID allocated to the corresponding network.
@@ -466,6 +484,16 @@
   oneway onEapFailure();
 
   /**
+   * Used to indicate the change of active bssid.
+   * This is useful to figure out when the driver/firmware roams to a bssid
+   * on its own.
+   *
+   * @param reason Reason why the bssid changed.
+   * @param bssid BSSID of the corresponding AP.
+   */
+  oneway onBssidChanged(BssidChangeReason reason, Bssid bssid);
+
+  /**
    * Used to indicate the success of a WPS connection attempt.
    */
   oneway onWpsEventSuccess();