binder: Implement |OnStateChanged| callback

Add state change callbacks. This is used by clients to monitor wpa_supplicant's
connection status, etc.

BUG: 30093041
TEST: Ran a simple connect/disconnect integration test gtest.

Change-Id: I35238f0f95b0a0a4723cb315ddaba30dd19d7dab
Signed-off-by: Roshan Pius <rpius@google.com>
diff --git a/wpa_supplicant/notify.c b/wpa_supplicant/notify.c
index b2b4225..61469dc 100644
--- a/wpa_supplicant/notify.c
+++ b/wpa_supplicant/notify.c
@@ -133,6 +133,8 @@
 		     wpa_ssid_txt(wpa_s->current_ssid->ssid,
 				  wpa_s->current_ssid->ssid_len) : "");
 #endif /* ANDROID */
+
+	wpas_binder_notify_state_changed(wpa_s);
 }