Fix struct io_iocb_sockaddr padding for 32bit architectures
    
    The io_iocb_sockaddr structure definition is missing padding for @addr
    and @len, which could result in -EINVAL being returned from
    io_submit() on applications compiled for 32 bit architectures.  Fix
    it.
    
    This was found after Brett reported a similar bug in the
    io_iocb_vector structure.
    
    Signed-off-by: Jeff Moyer <jmoyer@redhat.com>