The rfc doesn't give any reason it shouldn't be possible to set an
attribute on a non-regular file.  And if the server supports it, then it
shouldn't be up to us to prevent it.

Thanks to Erez for the report and Trond for further analysis.
Signed-off-by: NJ. Bruce Fields <bfields@citi.umich.edu>
Tested-by: NErez Zadok <ezk@cs.sunysb.edu>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>