Bug 960865 - Part 1: add dun apn type constant in idls. r=vchang
Bug 960865 - Part 2: handle dun apn type in RadioInterfaceLayer. r=hsinyi
Bug 960865 - Part 3: modify nat command to support setting rules for secondary routing table. r=vchang
Bug 960865 - Part 4: dun support implementation in NetworkManager. r=vchang
Bug 960865 - Part 5: add dun connection timer and reference count. r=vchang