This also refactors the BPF handling so it can be shared between the dhcp and farp plugins. The latter is adapted accordingly. Closes strongswan/strongswan#2047 Co-authored-by: Tobias Brunner <tobias@strongswan.org>
Co-authored-by: Tobias Brunner <tobias@strongswan.org> Closes strongswan/strongswan#189. References #3498.