LE: Add API to configure MTU for a given connection (1/4)

bug:13571470
Change-Id: Ia473998b714c3968c75565adeef20fef5656abb4
diff --git a/include/hardware/bt_gatt_client.h b/include/hardware/bt_gatt_client.h
index cf4fabe..11b146d 100644
--- a/include/hardware/bt_gatt_client.h
+++ b/include/hardware/bt_gatt_client.h
@@ -156,6 +156,9 @@
  */
 typedef void (*listen_callback)(int status, int server_if);
 
+/** Callback invoked when the MTU for a given connection changes */
+typedef void (*configure_mtu_callback)(int conn_id, int status, int mtu);
+
 typedef struct {
     register_client_callback            register_client_cb;
     scan_result_callback                scan_result_cb;
@@ -175,6 +178,7 @@
     execute_write_callback              execute_write_cb;
     read_remote_rssi_callback           read_remote_rssi_cb;
     listen_callback                     listen_cb;
+    configure_mtu_callback              configure_mtu_cb;
 } btgatt_client_callbacks_t;
 
 /** Represents the standard BT-GATT client interface. */
@@ -282,6 +286,9 @@
                     uint16_t service_data_len, char* service_data,
                     uint16_t service_uuid_len, char* service_uuid);
 
+    /** Configure the MTU for a given connection */
+    bt_status_t (*configure_mtu)(int conn_id, int mtu);
+
     /** Test mode interface */
     bt_status_t (*test_command)( int command, btgatt_test_params_t* params);
 } btgatt_client_interface_t;