[linux 5.10.0-rc2] variable slaac v1.7

Compatible linux kernel: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/tag/?h=v5.10-rc2
General networking (net-next) repo: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git

Changes:
some minor cross-compilation failure issues are addressed;
Readme: add section "Tests"