XMIT_CSUM_V6
#define XMIT_CSUM (XMIT_CSUM_V4 | XMIT_CSUM_V6 | XMIT_CSUM_ENC)
rc = XMIT_CSUM_V6;
if (xmit_type & (XMIT_CSUM_ENC_V6 | XMIT_CSUM_V6))