staging: slicoss depends on NET

The slicoss driver uses network interfaces so it should depend
on NET.  Fixes the following build errors:

ERROR: "eth_change_mtu" [drivers/staging/slicoss/slicoss.ko] undefined!
ERROR: "eth_validate_addr" [drivers/staging/slicoss/slicoss.ko] undefined!
ERROR: "register_netdev" [drivers/staging/slicoss/slicoss.ko] undefined!
ERROR: "alloc_etherdev_mqs" [drivers/staging/slicoss/slicoss.ko] undefined!
ERROR: "__netif_schedule" [drivers/staging/slicoss/slicoss.ko] undefined!
ERROR: "netif_rx" [drivers/staging/slicoss/slicoss.ko] undefined!
ERROR: "eth_type_trans" [drivers/staging/slicoss/slicoss.ko] undefined!
ERROR: "skb_put" [drivers/staging/slicoss/slicoss.ko] undefined!
ERROR: "skb_pull" [drivers/staging/slicoss/slicoss.ko] undefined!
ERROR: "__alloc_skb" [drivers/staging/slicoss/slicoss.ko] undefined!
ERROR: "free_netdev" [drivers/staging/slicoss/slicoss.ko] undefined!
ERROR: "unregister_netdev" [drivers/staging/slicoss/slicoss.ko] undefined!
ERROR: "consume_skb" [drivers/staging/slicoss/slicoss.ko] undefined!
ERROR: "dev_kfree_skb_irq" [drivers/staging/slicoss/slicoss.ko] undefined!

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Cc: Lior Dotan <liodot@gmail.com>
Cc: Christopher Harrer <charrer@alacritech.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>