ripd: split-horizon default differed between rip_interface_new and _reset

* rip_interface.c: Default for split_horizon_default differed between
  rip_interface_new and rip_interface_reset, causing at least some issues
  after interface events. See patchwork #604. Fix, and consolidate code.

  (rip_interface_{reset,clean}) rename these to 'interface', as that's more
  appropriate.  Spin the ri specific bodies of these functions out to
  rip_interface_{reset,clean} helpers.  Factor out the overlaps, so
  rip_interface_reset uses rip_interface_clean.

  (rip_interface_new) just use rip_interface_reset.

* ripd.h: Update for (rip_interface_{reset,clean})

Reported by xufeng zhang, with a suggested fix on which this commit expands.
See patchwork #604.  This commit addresses only the split-horizon
discrepency, issue #2.  The other issue they reported, #1, is not addressed,
though suggested fix seems inappropriate.

Cc: xufeng.zhang@windriver.com
diff --git a/ripd/ripd.c b/ripd/ripd.c
index 0beb0e6..1d3eb4c 100644
--- a/ripd/ripd.c
+++ b/ripd/ripd.c
@@ -4025,7 +4025,7 @@
   rip_clean_network ();
   rip_passive_nondefault_clean ();
   rip_offset_clean ();
-  rip_interface_clean ();
+  rip_interfaces_clean ();
   rip_distance_reset ();
   rip_redistribute_clean ();
 }
@@ -4049,7 +4049,7 @@
 
   distribute_list_reset ();
 
-  rip_interface_reset ();
+  rip_interfaces_reset ();
   rip_distance_reset ();
 
   rip_zclient_reset ();