../net/ipv6/addrconf.c: In function ‘addrconf_init’:
../net/ipv6/addrconf.c:6747:22: error: ‘blackhole_netdev’ undeclared (first use in this function); did you mean ‘alloc_netdev’?
  bdev = ipv6_add_dev(blackhole_netdev);
                      ^~~~~~~~~~~~~~~~
                      alloc_netdev
../net/ipv6/addrconf.c:6747:22: note: each undeclared identifier is reported only once for each function it appears in
../net/ipv6/addrconf.c: In function ‘addrconf_cleanup’:
../net/ipv6/addrconf.c:6839:18: error: ‘blackhole_netdev’ undeclared (first use in this function); did you mean ‘alloc_netdev’?
  addrconf_ifdown(blackhole_netdev, 2);
                  ^~~~~~~~~~~~~~~~
                  alloc_netdev
make[3]: *** [../scripts/Makefile.build:304: net/ipv6/addrconf.o] Error 1
../net/ipv6/route.c: In function ‘rt6_uncached_list_flush_dev’:
../net/ipv6/route.c:176:33: error: ‘blackhole_netdev’ undeclared (first use in this function); did you mean ‘alloc_netdev’?
     rt->rt6i_idev = in6_dev_get(blackhole_netdev);
                                 ^~~~~~~~~~~~~~~~
                                 alloc_netdev
../net/ipv6/route.c:176:33: note: each undeclared identifier is reported only once for each function it appears in
../net/ipv6/route.c:181:19: error: ‘loopback_dev’ undeclared (first use in this function); did you mean ‘local_dec’?
     rt->dst.dev = loopback_dev;
                   ^~~~~~~~~~~~
                   local_dec
../net/ipv6/route.c: In function ‘ip6_dst_ifdown’:
../net/ipv6/route.c:395:41: error: ‘blackhole_netdev’ undeclared (first use in this function); did you mean ‘alloc_netdev’?
   struct inet6_dev *ibdev = in6_dev_get(blackhole_netdev);
                                         ^~~~~~~~~~~~~~~~
                                         alloc_netdev
make[3]: *** [../scripts/Makefile.build:304: net/ipv6/route.o] Error 1
make[3]: Target '__build' not remade because of errors.
make[2]: *** [../scripts/Makefile.build:544: net/ipv6] Error 2
make[2]: Target '__build' not remade because of errors.
make[1]: *** [/srv/src/kernel/stable-v4.19/Makefile:1046: net] Error 2
make[1]: Target 'bzImage' not remade because of errors.
make: *** [Makefile:146: sub-make] Error 2
make: Target 'bzImage' not remade because of errors.