selftests: virtio_net: add forgotten config options

One may use tools/testing/selftests/drivers/net/virtio_net/config
for example for vng build command like this one:
$ vng -v -b -f tools/testing/selftests/drivers/net/virtio_net/config

In that case, the needed kernel config options are not turned on.
Add the missed kernel config options.
Reported-by: Jakub Kicinski <kuba@kernel.org>
Closes: https://lore.kernel.org/netdev/20240617072614.75fe79e7@kernel.org/Reported-by: Matthieu Baerts <matttbe@kernel.org>
Closes: https://lore.kernel.org/netdev/1a63f209-b1d4-4809-bc30-295a5cafa296@kernel.org/
Fixes: ccfaed04 ("selftests: virtio_net: add initial tests")
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://lore.kernel.org/r/20240619061748.1869404-1-jiri@resnulli.usSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/drivers/net/virtio_net/config

-CONFIG_VIRTIO_NET=y
+CONFIG_BPF_SYSCALL=y
+CONFIG_CGROUP_BPF=y
+CONFIG_IPV6=y
+CONFIG_IPV6_MULTIPLE_TABLES=y
+CONFIG_NET_L3_MASTER_DEV=y
+CONFIG_NET_VRF=m
 CONFIG_VIRTIO_DEBUG=y
+CONFIG_VIRTIO_NET=y