NFS: Fix handling of reply page vector

NFSv4 GETACL and FS_LOCATIONS requests stopped working in v5.1-rc.

These two need the extra padding to be added directly to the reply
length.

Reported-by: Olga Kornievskaia <aglo@umich.edu>
Fixes: 02ef04e4 ("NFS: Account for XDR pad of buf->pages")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Olga Kornievskaia <aglo@umich.edu>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>