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/socket.h b/osi/include/socket.h
index 2833290..ac49921 100644
--- a/osi/include/socket.h
+++ b/osi/include/socket.h
@@ -23,6 +23,10 @@
 #include <stdint.h>
 #include <sys/types.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 typedef struct reactor_t reactor_t;
 typedef struct socket_t socket_t;
 typedef uint16_t port_t;
@@ -98,3 +102,7 @@
 // Unregisters |socket| from whichever reactor it is registered with, if any. This
 // function is idempotent.
 void socket_unregister(socket_t *socket);
+
+#ifdef __cplusplus
+}
+#endif
\ No newline at end of file