net/netdev: remove unnecessary sleep when netdev_ifup()
net/netdev: remove unnecessary sleep when netdev_ifup()

This removes unnecessary 3 seconds sleep for interface up.

Change-Id: I3c63b5c0a14892441abc224409b9a1ad8b76faa1
Signed-off-by: Siwon Kang <ebec45d95c8f1b394ce3a1fc19033d35a81f3ab6@samsung.com>

JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT