net, team, bonding: Add netdev_base_features helper

Both bonding and team driver have logic to derive the base feature
flags before iterating over their slave devices to refine the set
via netdev_increment_features().

Add a small helper netdev_base_features() so this can be reused
instead of having it open-coded multiple times.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Nikolay Aleksandrov <razor@blackwall.org>
Cc: Ido Schimmel <idosch@idosch.org>
Cc: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/20241210141245.327886-1-daniel@iogearbox.net


Signed-off-by: Paolo Abeni <pabeni@redhat.com>