net: socket: Add support for setting pktinfo options

Add IP_PKTINFO or IPV6_RECVPKTINFO BSD socket options that
can be used to get extra information of received data in
the ancillary data in recvmsg() call.

For IPV6_RECVPKTINFO see RFC 3542 for details.
For IP_PKTINFO see Linux ip(7) manual page for details.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>