This also fixes a bug in sending ihu intervals.

We send hellos with a very short lifetime when leaving the network.
This was broken when I implemented automatically adjusting the hello
interval.

  - Fusion de kernel_listen dans kernel_read.
  - Fusion de monitor_kernel_routes dans filter_kernel_routes.
  - En cas d'erreur d'entree/sortie on ferme les sockets.
    - nl_command est rouverte au besoin
    - nl_listen doit etre rouverte a l'aide de kernel_setup_socket(1)

This is not compatible with version 0.  Uses 24-byte messages and
doesn't distinguish routes from xroutes.

This avoids inconsistent routing if a neighbour is ingress filtering a
route.