netdevsim: dev: Initialize FIB module after debugfs

Initialize the dummy FIB offload module after debugfs, so that the FIB
module could create its own directory there.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>