Add additional checks for IPV6_PKTINFO handling (RFC 3542):

• Return ENETDOWN when interface specified by ipi6_ifindex is not enabled for IPv6 use.
• Return EADDRNOTAVAIL when ipi6_ifindex specifies an interface, but the address ipi6_addr is not available for use on that interface.
• Return EINVAL when ipi6_addr is multicast address.

Obtained from: Yandex LLC
Sponsored by: Yandex LLC