OpenBSD does not support TCP_KEEPALIVE/TCP_KEEPINTVL with SO_KEEPALIVE turned ON.
Using SO_KEEPALIVE/TCP_KEEPALIVE on a IPPROTO_TCP level is not supported on OpenBSD. OpenBSD only supports global sysctl settings for setting the keepalive intervals:
net.inet.tcp.keepinittime=150
net.inet.tcp.keepidle=14400
net.inet.tcp.keepintvl=150
net.inet.tcp.always_keepalive=0
Thus breaking the compilation