* ospf_packet.h: Remove commented out definition of
OSPF_MAX_PACKET; neither it or the uncommented one are used any more.
* ospf_packet.c (ospf_make_ls_upd): Leave room for authentication
when deciding if an update will fit.
(ospf_packet_authspace): Factor out calculation of size required
for authentication.
(ospf_make_db_desc): Use ospf_max_packet, not OSPF_MAX_PACKET.
Don't confuse readers that there is a macro.