ospfd: Fix bug in 94266fa822ba, nbr_self rebuild didn't add valid nbr_self

ospfd: Fix bug in 94266fa822ba, nbr_self rebuild didn't add valid nbr_self

* 94266fa822ba "ospfd: Self nbrs needs to be rebuilt when router ID changes."
  deleted the nbr_self, and added it back, but ospf_nbr_add_self doesn't
  actually create the nbr_self - it assumes it's already there. Leading
  to use after free and crashes after a router-id change.
* ospfd/ospf_neighbor.{c,h}: (ospf_nbr_self_reset) Little helper to reset the
  nbr_self correctly.
* ospf_interface.c: (ospf_if_cleanup) moved code to ospf_nbr_self_reset
* ospfd.c: (ospf_router_id_update) Use ospf_nbr_self_reset instead of doing
  the reset badly, fixing 94266fa822ba.

(cherry picked from commit c920e510d09c6c4ab63a3da5375009442a950f82)