net: Change dev parameter to const in netif_device_present()

Not all ndos check the present bit before calling the ndo and the driver
may want to check it. Sometimes the dev parameter passed as const so we
pass it to netif_device_present() as const.
Since netif_device_present() doesn't modify dev parameter anyway, declare
it as const.

Signed-off-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>