l2tp: read IPv6 UDP checksum attributes from kernel

In case of an older kernel that doesn't set L2TP_ATTR_UDP_ZERO_CSUM6_{RX,TX}
the old hard-coded value is being preserved, since the attribute flag will be
missing.

Signed-off-by: Asbjørn Sloth Tønnesen <asbjorn@asbjorn.st>
1 file changed