bluetooth: silence compiler warning (missing writev(2) declaration)

src/bt/bt_bluez.c

@@ -79,6 +79,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/uio.h>
 #include <sys/socket.h>
 #include <time.h>
 #include <unistd.h>