The package python-scapy3k (https://github.com/buildroot/buildroot/blob/master/package/python-scapy3k/python-scapy3k.mk) is deprecated since python-scapy supports Python 3 (v2.4.0+).
Thanks for this report. Feel free to send a patch to the mailing list to remove python-scapy3k. Make sure to also include legacy handling (i.e. move the option to Config.in.legacy and select BR2_PACKAGE_PYTHON_SCAPY from it).
Thanks for the answer. I've submitted a patch: http://lists.busybox.net/pipermail/buildroot/2019-December/268075.html
Fixed by https://git.buildroot.org/buildroot/commit/?id=689ba599d0eb99d9864d264484bff01da250eb98. Thanks!