vrf: mark skb for multicast or link-local as enslaved to VRF

The skb for packets that are multicast or to a link-local address are
not marked as being enslaved to a VRF, if they are received on a socket
bound to the VRF. This is needed for ND and it is preferable for the
kernel not to have to deal with the additional use-cases if ll or mcast
packets are handled as enslaved. However, this does not allow service
instances listening on unbound and bound to VRF sockets to distinguish
the VRF used, if packets are sent as multicast or to a link-local
address. The fix is for the VRF driver to also mark these skb as being
enslaved to the VRF.

Signed-off-by: Mike Manning <mmanning@vyatta.att-mail.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Tested-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>