Include missing headers

Bug: None
Test: Build
Change-Id: Id4967af4ab48ceda10c45edcb0bc4b856b991fd6
diff --git a/bluetooth/1.0/default/bluetooth_hci.h b/bluetooth/1.0/default/bluetooth_hci.h
index 6912405..e2797b1 100644
--- a/bluetooth/1.0/default/bluetooth_hci.h
+++ b/bluetooth/1.0/default/bluetooth_hci.h
@@ -21,6 +21,8 @@
 
 #include <hidl/MQDescriptor.h>
 
+#include <functional>
+
 namespace android {
 namespace hardware {
 namespace bluetooth {