fddi: 64 bit bug in smt_add_para()

The intent was to set 4 bytes of data so that's why the sp_len is set
to 4 on the next line.  The cast to u_long pointer clears 8 bytes
on 64 bit arches.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@tempietto.lan>