netdev-genl: fix repeated typo oflloading -> offloading

Fix a repeated copy/paste typo.

Fixes: d3d854fd ("netdev-genl: create a simple family for netdev stuff")
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>