nfs: only show Posix ACLs in listxattr if actually present

nfs: only show Posix ACLs in listxattr if actually present

The big ACL switched nfs to use generic_listxattr, which calls all existing
->list handlers.  Add a custom .listxattr implementation that only lists
the ACLs if they actually are present on the given inode.

Signed-off-by: Christoph Hellwig <[email protected]>
Reported-by: Philippe Troin <[email protected]>
Tested-by: Philippe Troin <[email protected]>
Fixes: 013cdf1088d7 (nfs: use generic posix ACL infrastructure ...)
Cc: [email protected] # 3.14+
Signed-off-by: Trond Myklebust <[email protected]>