SRC_FLAG_BIT
const uint32_t tid = A & (SRC_FLAG_BIT - 1);
addr = npc->npc_ips[(A & SRC_FLAG_BIT) ? NPF_SRC : NPF_DST];
BPF_STMT(BPF_LD+BPF_IMM, (src ? SRC_FLAG_BIT : 0) | tid),