netinet/in.h: add IPV6_ROUTER_ALERT_ISOLATE from linux v5.1

restricts router alert packets received by the socket to the
socket's namespace only. see

  linux commit 9036b2fe092a107856edd1a3bad48b83f2b45000
  net: ipv6: add socket option IPV6_ROUTER_ALERT_ISOLATE
1 file changed