Support receiving, extracting flow key and sending of L3 packets (packets
without an Ethernet header).

Note that even after this patch, non-Ethernet interfaces are still not
allowed to be added to bridges. Similarly, netlink interface for sending and
receiving L3 packets to/from user space is not in place yet.

Based on previous versions by Lorand Jakab and Simon Horman.
Signed-off-by: NLorand Jakab <lojakab@cisco.com>
Signed-off-by: NSimon Horman <simon.horman@netronome.com>
Signed-off-by: NJiri Benc <jbenc@redhat.com>
Acked-by: NPravin B Shelar <pshelar@ovn.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>