sunrpc: don't shorten buflen twice in xdr_shrink_pagelen

On Jan. 14, 2009, 2:50 +0200, andros@netapp.com wrote:
> From: Andy Adamson <andros@netapp.com>
>
> The buflen is reset for all cases at the end of xdr_shrink_pagelen.
> The data left in the tail after xdr_read_pages is not processed when the
> buflen is incorrectly set.

Note that in this case we also lose (len - tail->iov_len)
bytes from the buffered data in pages.

Reported-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>