netdev-genl: Add netlink framework functions for napi

Implement the netdev netlink framework functions for
napi support. The netdev structure tracks all the napi
instances and napi fields. The napi instances and associated
parameters can be retrieved this way.

Signed-off-by: Amritha Nambiar <amritha.nambiar@intel.com>
Reviewed-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
Link: https://lore.kernel.org/r/170147333637.5260.14807433239805550815.stgit@anambiarhost.jf.intel.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>