Build android.hardware.bluetooth* modules with BOARD_VNDK_VERSION

Add missing headers that aren't automatically included when
BOARD_VNDK_VERSION is set.

Bug: 37342627
Test: BOARD_VNDK_VERSION=current m -j <module> where <module> is
android.hardware.bluetooth-async.vendor,
android.hardware.bluetooth@1.0-impl.vendor, and
android.hardware.bluetooth-hci.vendor

Change-Id: Ifb14d254fa358fbd2b9fbeecb028d6efd18e9483
diff --git a/bluetooth/1.0/default/hci_protocol.cc b/bluetooth/1.0/default/hci_protocol.cc
index 5d6f1d1..bf94dfe 100644
--- a/bluetooth/1.0/default/hci_protocol.cc
+++ b/bluetooth/1.0/default/hci_protocol.cc
@@ -20,6 +20,7 @@
 #include <assert.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <unistd.h>
 #include <log/log.h>
 
 namespace android {