nfp: allow fallback packets from non-reprs

Currently, it is assumed that fallback packets will be from reprs. Modify
this to allow an app to receive non-repr ports from the fallback channel -
e.g. from an internal port. If such a packet is received, do not update
repr stats.

Change the naming function calls so as not to imply it will always be a
repr netdev returned. Add the option to set a bool value to redirect a
fallback packet out the returned port rather than RXing it. Setting of
this bool in subsequent patches allows the handling of packets falling
back when they are due to egress an internal port.

Signed-off-by: John Hurley <john.hurley@netronome.com>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>