nfp: flower: increase scope of netdev checking functions

Both the actions and tunnel_conf files contain local functions that check
the type of an input netdev. In preparation for re-use with tunnel offload
via indirect blocks, move these to static inline functions in a header
file.

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