MAINTAINERS: Add netkit selftest files

MAINTAINERS: Add netkit selftest files

The following selftest files are related to netkit and should have
netkit folks in Cc for review:

  - tools/testing/selftests/bpf/prog_tests/tc_netkit.c
  - tools/testing/selftests/drivers/net/hw/nk_qlease.py
  - tools/testing/selftests/net/nk_qlease.py

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/20260414075249.611608-1-daniel@iogearbox.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>