vrf: prevent adding upper devices

VRF devices don't work with upper devices. Currently, it's possible to
add a VRF device to a bridge or team, and to create macvlan, macsec, or
ipvlan devices on top of a VRF (bond and vlan are prevented respectively
by the lack of an ndo_set_mac_address op and the NETIF_F_VLAN_CHALLENGED
feature flag).

Fix this by setting the IFF_NO_RX_HANDLER flag (introduced in commit
f5426250 ("net: introduce IFF_NO_RX_HANDLER")).

Cc: David Ahern <dsahern@gmail.com>
Fixes: 193125db

 ("net: Introduce VRF device driver")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Acked-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>