orangefs: off by ones in xattr size checks

A previous patch which claimed to remove off by ones actually introduced
them.

strlen() returns the length of the string not including the NUL
character.  We are using strcpy() to copy "name" into a buffer which is
ORANGEFS_MAX_XATTR_NAMELEN characters long.  We should make sure to
leave space for the NUL, otherwise we're writing one character beyond
the end of the buffer.

Fixes: e675c5ec

 ("orangefs: clean up oversize xattr validation")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mike Marshall <hubcap@omnibond.com>