dev can be a NULL here, not all requests set require_dev.

Fixes: e4b89540 ("netlink: add net device refcount tracker to struct ethnl_req_info")
Signed-off-by: NJakub Kicinski <kuba@kernel.org>
Reviewed-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>