Convert BTIF code from C to C++

Modifications required:
 * added proper casting
 * moved variable definitions before goto statements
 * added 'extern "C"' markers where needed
 * renamed 'operator' to 'operator_name'

Bug: 28485365
Change-Id: I903357967387207e678866c02e008f047f8263f6
diff --git a/osi/include/fixed_queue.h b/osi/include/fixed_queue.h
index 1fb1b4b..a125336 100644
--- a/osi/include/fixed_queue.h
+++ b/osi/include/fixed_queue.h
@@ -23,6 +23,10 @@
 
 #include "osi/include/list.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 struct fixed_queue_t;
 typedef struct fixed_queue_t fixed_queue_t;
 typedef struct reactor_t reactor_t;
@@ -122,3 +126,7 @@
 // Unregisters the dequeue ready callback for |queue| from whichever reactor
 // it is registered with, if any. This function is idempotent.
 void fixed_queue_unregister_dequeue(fixed_queue_t *queue);
+
+#ifdef __cplusplus
+}
+#endif