lib: Add a function to delete all interfaces

if.c: (if_terminate) This adds a cleanup function that can be called
    when a daemon exits, similar to vty_terminate().
diff --git a/lib/if.c b/lib/if.c
index 41115b0..31c60e3 100644
--- a/lib/if.c
+++ b/lib/if.c
@@ -872,3 +872,21 @@
 
   memset (&if_master, 0, sizeof if_master);
 }
+
+void
+if_terminate (void)
+{
+  for (;;)
+    {
+      struct interface *ifp;
+
+      ifp = listnode_head (iflist);
+      if (ifp == NULL)
+	break;
+
+      if_delete (ifp);
+    }
+
+  list_delete (iflist);
+  iflist = NULL;
+}
diff --git a/lib/if.h b/lib/if.h
index c99ab81..841ce51 100644
--- a/lib/if.h
+++ b/lib/if.h
@@ -266,6 +266,7 @@
 extern int if_is_multicast (struct interface *);
 extern void if_add_hook (int, int (*)(struct interface *));
 extern void if_init (void);
+extern void if_terminate (void);
 extern void if_dump_all (void);
 extern const char *if_flag_dump(unsigned long);