Allowed optimized exporting of a subprefix tree

Added an option for export filter to allow for prefiltering based on the
prefix. Routes outside the given prefix are completely ignored. Config
is simple:

	export in <net> <filter>;

1 files changed, 6 insertions, 0 deletions

diff --git a/nest/config.Y b/nest/config.Y
index ea7e1266..c3f2532f 100644
--- a/nest/config.Y
+++ b/nest/config.Y
@@ -306,6 +306,12 @@ channel_item_:
      this_channel->table = $2;
    }
  | IMPORT imexport { this_channel->in_filter = $2; }
+ | EXPORT IN net_any imexport {
+     if (this_channel->net_type && ($3->type != this_channel->net_type))
+       cf_error("Incompatible export prefilter type");
+     this_channel->out_subprefix = $3;
+     this_channel->out_filter = $4;
+   }
  | EXPORT imexport { this_channel->out_filter = $2; }
  | RECEIVE LIMIT limit_spec { this_channel->rx_limit = $3; }
  | IMPORT LIMIT limit_spec { this_channel->in_limit = $3; }