corerouter: use patched version of bird2 and add proper inbound metrics

Switch to using a patched version of the BIRD daemon (`bird2-babelpatch`)
maintained in our own repository. This version includes modifications to the
Babel protocol, allowing route filtering based on specific interfaces and
neighbors, while exporting all Babel routes to BIRD's core for enhanced
flexibility.

Link: https://bird.network.cz/pipermail/bird-users/2023-February/016705.html
Link: #1087

group_vars/role_corerouter/imageprofile.yml

@@ -1,6 +1,6 @@
 ---
 role_corerouter__packages__to_merge:
-  - bird2
+  - bird2-babelpatch
   - bird2c
   - collectd-mod-dhcpleases
   - collectd-mod-olsrd

roles/cfg_openwrt/templates/corerouter/bird.conf.j2

@@ -27,7 +27,23 @@ protocol babel {
 	ipv6 sadr {
 		table v6_main;
 		# Import only /56 location aggregates and default routes
-		import where (net.len = 56) || (net = ::/0 from {{ freifunk_global_prefix }} );
+		import filter {
+			if ! (net.len = 56 || net = ::/0 from {{ freifunk_global_prefix }}) then reject;
+{% for nw in networks | selectattr('role', 'equalto', 'mesh') %}
+  {# metrics for 2 GHz adhoc get a penalty over 5 GHz adhoc so 5 GHz is preferred #}
+  {% set default_mesh_metric = hostvars[inventory_hostname].get('mesh_metric_adhoc_' ~ nw.get('mesh_radio'), mesh_metric_default_in) %}
+			if ifname = "{{ libnetwork.getIfname(nw) }}" then {
+			  babel_metric = babel_metric + {{  nw.get('mesh_metric', default_mesh_metric) }};
+			}
+{% endfor %}
+{% for nw in networks | selectattr('role', 'equalto', 'tunnel') %}
+			if ifname = "{{ nw.get('ifname') }}" then {
+			  babel_metric = babel_metric + {{  nw.get('mesh_metric', mesh_metric_tunnel_in) }};
+			}
+{% endfor %}
+			accept;
+		};
+
 		export filter {
 			if net = {{ ipv6_prefix }} from ::/0 then accept;
 			if source = RTS_BABEL then accept;
@@ -40,19 +56,15 @@ protocol babel {
 	};
 
 	# Mesh interfaces
-{# metrics for 2 GHz adhoc get a penalty over 5 GHz adhoc so 5 GHz is preferred #}
 {% for nw in networks | selectattr('role', 'equalto', 'mesh') %}
-  {% set default_mesh_metric = hostvars[inventory_hostname].get('mesh_metric_adhoc_' ~ nw.get('mesh_radio'), mesh_metric_default_in) %} 
 	interface "{{ libnetwork.getIfname(nw) }}" {
 		type wireless;
-		rxcost {{ nw.get('mesh_metric', default_mesh_metric) }};
 	};
 {% endfor %}
 	# Tunnel interfaces provided by tunspace
 {% for nw in networks | selectattr('role', 'equalto', 'tunnel') %}
 	interface "{{ nw.get('ifname') }}" {
 		type wireless;
-		rxcost {{ nw.get('mesh_metric', mesh_metric_tunnel_in) }};
 	};
 {% endfor %}
 }