Update network.lua

Update network.lua

Fix display of WAN status when WAN is provided by using WWAN device or similar with other similar similar methods.
Explanation:
Before this, protocol was fetched from /etc/config/network for interface which often is wan_4 - but protocol is configured in file as wan, and therefore protocol is always none, since configuration is made for wan and then setup as wan_4 and possibly wan_6 if ipv6 is being used. This commit uses ubus to get used active protocol. For example, in case of qmi, it displays protocol as dhcp since even if I configured wan to use qmi, dhcp was used as a protocol for getting IP address.