eth: iavf: extend the netdev_lock usage

eth: iavf: extend the netdev_lock usage

iavf uses the netdev->lock already to protect shapers.
In an upcoming series we'll try to protect NAPI instances
with netdev->lock.

We need to modify the protection a bit. All NAPI related
calls in the driver need to be consistently under the lock.
This will allow us to easily switch to a "we already hold
the lock" NAPI API later.

register_netdevice(), OTOH, must not be called under
the netdev_lock() as we do not intend to have an
"already locked" version of this call.

Link: https://patch.msgid.link/20250111071339.3709071-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>