luci-base: consolidate network.js data acquisition

The new luci-rpc/getNetworkDevices procedure offers netdev enumeration
with included IPv4 and IPv6 address information as well as 64bit traffic
counters, so we can remove the calls to network.device/status and
luci/getIfaddrs now as we're able to obtain all info from a single source.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>