Set destination for PtP links to OSPF_ALLSPFROUTERS.

Set destination for PtP links to OSPF_ALLSPFROUTERS.

Update ospf_db_desc_send(), ospf_ls_upd_queue_send() and ospf_ls_req_send()
to always use OSPF_ALLSPFROUTERS for PtP links.

See RFC 2328, chap 8.1 for details:

    "The IP destination address for the packet is selected as
     follows.  On physical point-to-point networks, the IP
     destination is always set to the address AllSPFRouters."

Without this, it won't be possible to establish adjacencies on
multiple unnumbered links to the same router.
ChangeLog:
2008-07-25 Joakim Tjernlund <Joakim.Tjernlund@transmode.se>

	* ospfd/ospf_packet.c: Set destination for PtP links to
	  OSPF_ALLSPFROUTERS.