data cache invalidation on delegation recalls

when we receive a delegation recall, we need to make a downcall
to the kernel and change a buffering/caching policy on this file.

on each open and close we pass an srv_open pointer to the nfsd to
keep in case it receives a cb_recall. we store srv_open in the
delegation state if we got a delegation.

daemon/upcall.h

@@ -54,11 +54,13 @@ typedef struct __open_upcall_args {
     LONG open_owner_id;
     DWORD mode;
     LONGLONG changeattr;
+    HANDLE srv_open;
     BOOLEAN created;
     BOOLEAN symlink_embedded;
 } open_upcall_args;
 
 typedef struct __close_upcall_args {
+    HANDLE srv_open;
     const char *path;
     BOOLEAN remove;
     BOOLEAN renamed;