MINOR: compression: add an offload option to remove the Accept-Encoding header

This is used when it is desired that backend servers don't compress
(eg: because of buggy implementations).
diff --git a/include/types/compression.h b/include/types/compression.h
index 96dd107..10ac4b1 100644
--- a/include/types/compression.h
+++ b/include/types/compression.h
@@ -28,6 +28,7 @@
 struct comp {
 	struct comp_algo *algos;
 	struct comp_type *types;
+	unsigned int offload;
 };
 
 struct comp_algo {