MFC r322310:
Add to if_enc(4) ability to capture packets via BPF after pfil processing. New flag 0x4 can be configured in net.enc.[in|out].ipsec_bpf_mask. When it is set, if_enc(4) additionally captures a packet via BPF after invoking pfil hook. This may be useful for debugging. Sponsored by: Yandex LLC