nixos-module/container/bird: become designated router for ospf instances when adveritising upstream

nix/nixos-module/container/bird.nix

@@ -144,6 +144,8 @@ in
       ${lib.optionalString isUpstream ''
         # OSPFv2 to advertise my default route
         protocol ospf v2 ZW4_${hostName} {
+          # Become the designated router
+          priority 10;
           ipv4 {
             export where net = 0.0.0.0/0;
           };
@@ -244,6 +246,8 @@ in
       ${lib.optionalString isUpstream ''
         # OSPFv3 to advertise my default route
         protocol ospf v3 ZW6_${hostName} {
+          # Become the designated router
+          priority 10;
           ipv6 {
             export where net = ::/0;
           };