ospfd: Remember network LSA sequence numbers across up/downs of an interface

* ospf_interface.h: (struct ospf_if_params) add field for saved network LSA
  seqnum
* ospf_interfa.c: (ospf_new_if_params) init network_lsa_seqnum field to
  initial seqnum - doesnt matter though.
* ospf_lsa.c: (ospf_network_lsa_new) check for any saved sequence number,
  and use if it exists.  Save the result back. This should help avoid needless
  round of LSUpdate/LSRequests when a neighbour has to tell the originator
  "uhm, i have something newer than that already".
* ospf_vty.c: (show_ip_ospf_interface_sub) Show the saved network LSA seqnum
diff --git a/ospfd/ospf_interface.c b/ospfd/ospf_interface.c
index b333658..a812dd9 100644
--- a/ospfd/ospf_interface.c
+++ b/ospfd/ospf_interface.c
@@ -531,6 +531,8 @@
 
   oip->auth_crypt = list_new ();
   
+  oip->network_lsa_seqnum = htonl(OSPF_INITIAL_SEQUENCE_NUMBER);
+
   return oip;
 }
 
@@ -569,7 +571,8 @@
       !OSPF_IF_PARAM_CONFIGURED (oip, type) &&
       !OSPF_IF_PARAM_CONFIGURED (oip, auth_simple) &&
       !OSPF_IF_PARAM_CONFIGURED (oip, auth_type) &&
-      listcount (oip->auth_crypt) == 0)
+      listcount (oip->auth_crypt) == 0 &&
+      ntohl (oip->network_lsa_seqnum) != OSPF_INITIAL_SEQUENCE_NUMBER)
     {
       ospf_del_if_params (oip);
       rn->info = NULL;
diff --git a/ospfd/ospf_interface.h b/ospfd/ospf_interface.h
index ab0b758..f495c49 100644
--- a/ospfd/ospf_interface.h
+++ b/ospfd/ospf_interface.h
@@ -73,6 +73,9 @@
   
   DECLARE_IF_PARAM (struct list *, auth_crypt);    /* List of Auth cryptographic data. */
   DECLARE_IF_PARAM (int, auth_type);               /* OSPF authentication type */
+  
+  /* Other, non-configuration state */
+  u_int32_t network_lsa_seqnum;		/* Network LSA seqnum */
 };
 
 enum
@@ -167,6 +170,7 @@
 
   /* Configured varables. */
   struct ospf_if_params *params;
+  
   u_int32_t crypt_seqnum;		/* Cryptographic Sequence Number */ 
   u_int32_t output_cost;	        /* Acutual Interface Output Cost */
 
diff --git a/ospfd/ospf_lsa.c b/ospfd/ospf_lsa.c
index 0c23909..ec736fc 100644
--- a/ospfd/ospf_lsa.c
+++ b/ospfd/ospf_lsa.c
@@ -1048,6 +1048,7 @@
   struct stream *s;
   struct ospf_lsa *new;
   struct lsa_header *lsah;
+  struct ospf_if_params *oip;
   int length;
 
   /* If there are no neighbours on this network (the net is stub),
@@ -1086,7 +1087,23 @@
   new->data = ospf_lsa_data_new (length);
   memcpy (new->data, lsah, length);
   stream_free (s);
-
+  
+  /* Remember prior network LSA sequence numbers, even if we stop
+   * originating one for this oi, to try avoid re-originating LSAs with a
+   * prior sequence number, and thus speed up adjency forming & convergence.
+   */
+  if ((oip = ospf_lookup_if_params (oi->ifp, oi->address->u.prefix4)))
+    {
+      new->data->ls_seqnum = oip->network_lsa_seqnum;
+      new->data->ls_seqnum = lsa_seqnum_increment (new);
+    }
+  else
+    {
+      oip = ospf_get_if_params (oi->ifp, oi->address->u.prefix4);
+      ospf_if_update_params (oi->ifp, oi->address->u.prefix4);
+    }
+  oip->network_lsa_seqnum = new->data->ls_seqnum;
+  
   return new;
 }
 
@@ -1125,6 +1142,7 @@
 {
   struct ospf_area *area = lsa->area;
   struct ospf_lsa *new;
+  struct ospf_if_params *oip;
 
   assert (lsa->data);
 
@@ -1135,7 +1153,10 @@
   new = ospf_network_lsa_new (oi);
   if (new == NULL)
     return -1;
-  new->data->ls_seqnum = lsa_seqnum_increment (lsa);
+  
+  oip = ospf_lookup_if_params (oi->ifp, oi->address->u.prefix4);
+  assert (oip != NULL);
+  oip->network_lsa_seqnum = new->data->ls_seqnum = lsa_seqnum_increment (lsa);
 
   ospf_lsa_install (area->ospf, oi, new);
 
diff --git a/ospfd/ospf_vty.c b/ospfd/ospf_vty.c
index adc822a..4e52a11 100644
--- a/ospfd/ospf_vty.c
+++ b/ospfd/ospf_vty.c
@@ -2933,7 +2933,13 @@
 		       inet_ntoa (nbr->address.u.prefix4), VTY_NEWLINE);
 	    }
 	}
-
+      
+      /* Next network-LSA sequence number we'll use, if we're elected DR */
+      if (oi->params && ntohl (oi->params->network_lsa_seqnum)
+                          != OSPF_INITIAL_SEQUENCE_NUMBER)
+        vty_out (vty, "  Saved Network-LSA sequence number 0x%x%s",
+                 ntohl (oi->params->network_lsa_seqnum), VTY_NEWLINE);
+      
       vty_out (vty, "  Multicast group memberships:");
       if (OI_MEMBER_CHECK(oi, MEMBER_ALLROUTERS)
           || OI_MEMBER_CHECK(oi, MEMBER_DROUTERS))