SUNRPC: introduce cache_detail->cache_request callback

This callback will allow to simplify upcalls in further patches in this
series.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

include/linux/sunrpc/cache.h

@@ -83,6 +83,10 @@ struct cache_detail {
 	int			(*cache_upcall)(struct cache_detail *,
 						struct cache_head *);
 
+	void			(*cache_request)(struct cache_detail *cd,
+						 struct cache_head *ch,
+						 char **bpp, int *blen);
+
 	int			(*cache_parse)(struct cache_detail *,
 					       char *buf, int len);