ospfd: Make sure route table is recalculated.

ospfd: Make sure route table is recalculated.

In some cases ospfd does not recalc the route table. This
happens when ospfd receives an old LSA which will trigger
recalc but the this recalc will fail because all interfaces
isn't up yet. Next LSA that is originated matches the old one
so no recalc will be performed. This problem has been observed
when there are only 2 ppp I/Fs in an area, both go down at the
same time, then they come up again with a few seconds apart.

* ospf_lsa.c: (ospf_{router,network}_lsa_install) avoid a needless scheduling
  of SPF.
  (ospf_lsa_different) fix bug in LSA comparison that would lead to the
  described failure to schedule SPF.