From: Andreas Gruenbacher <agruen@suse.de>

The getxattr (listxattr) syscall returns E2BIG if the buffer passed to them
is bigger than XATTR_SIZE_MAX (XATTR_LIST_MAX), no matter what buffer size is
actually required.  Here is a fix.  It also removes the xattr_alloc and
xattr_free functions which are not of much use anymore.