libnfs-private.h: wrap in extern "C" for C++ compatibility

Signed-off-by: Arne Redlich <arne.redlich@googlemail.com>

include/libnfs-private.h

@@ -28,6 +28,9 @@
 
 #include "libnfs-zdr.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 #if !defined(HAVE_SOCKADDR_STORAGE) && !defined(WIN32)
 /*
@@ -154,4 +157,8 @@ void rpc_free_all_fragments(struct rpc_context *rpc);
 
 const struct nfs_fh3 *nfs_get_rootfh(struct nfs_context *nfs);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* !_LIBNFS_PRIVATE_H_ */