Ubuntu 14.04 Dell Latitude E7470 Wifi and Ethernet not working

Question

I got a Dell Latitude E7470 which came by default with Ubuntu 1404 preinstalled. On day 1, Wi-Fi worked perfectly, but on day 2 after accepting one of the recommended software updates it stopped working altogether. The laptop cannot recognize and display any available network. Further, the ethernet is also not working, which is also a problem on its own and makes it more difficult to install any missing drivers since I have no connection at all.

While searching online, I found this scheme to install drivers offline. I don't have the installation disk so I used the links there. It didn't work though (after reboot). How to install Broadcom wireless drivers offline?

I think I'd really need some specific help from hereon. At the moment, I am moving back and forth the output of command lines from the faulty machine and this other one where I have connection. Here is some info that proved useful in other similar Ubuntu/internet problems:

Output of lspci

00:00.0 Host bridge: Intel Corporation Sky Lake Host Bridge/DRAM Registers (rev 08)
00:02.0 VGA compatible controller: Intel Corporation Sky Lake Integrated Graphics (rev 07)
00:04.0 Signal processing controller: Intel Corporation Device 1903 (rev 08)
00:14.0 USB controller: Intel Corporation Device 9d2f (rev 21)
00:14.2 Signal processing controller: Intel Corporation Device 9d31 (rev 21)
00:16.0 Communication controller: Intel Corporation Device 9d3a (rev 21)
00:17.0 SATA controller: Intel Corporation Device 9d03 (rev 21)
00:1c.0 PCI bridge: Intel Corporation Device 9d14 (rev f1)
00:1d.0 PCI bridge: Intel Corporation Device 9d1a (rev f1)
00:1f.0 ISA bridge: Intel Corporation Device 9d48 (rev 21)
00:1f.2 Memory controller: Intel Corporation Device 9d21 (rev 21)
00:1f.3 Audio device: Intel Corporation Device 9d70 (rev 21)
00:1f.4 SMBus: Intel Corporation Device 9d23 (rev 21)
00:1f.6 Ethernet controller: Intel Corporation Ethernet Connection I219-LM (rev 21)
01:00.0 Network controller: Intel Corporation Wireless 8260 (rev 3a)
02:00.0 Unassigned class [ff00]: Realtek Semiconductor Co., Ltd. Device 525a (rev 01)

Output of lshw -C network:

*-network UNCLAIMED
   description: Network controller
   product: Wireless 8260
   vendor: Intel Corporation
   physical id: 0
   bus info: pci@0000:01:00.0
   version: 3a
   width: 64 bits
   clock: 33MHz
   capabilities: pm msi pciexpress cap_list
   configuration: latency=0
   resources: memory:e1100000-e1101fff
*-network UNCLAIMED
   description: Ethernet controller
   product: Ethernet Connection I219-LM
   vendor: Intel Corporation
   physical id: 1f.6
   bus info: pci@0000:00:1f.6
   version: 21
   width: 32 bits
   clock: 33MHz
   capabilities: pm msi cap_list
   configuration: latency=0
   resources: memory:e1200000-e121ffff

Output of nm-tool:

NetworkManager Tool

State: disconnected

Output of ifconfig -a:

lo        Link encap:Local Loopback  
      inet addr:127.0.0.1  Mask:255.0.0.0
      inet6 addr: ::1/128 Scope:Host
      UP LOOPBACK RUNNING  MTU:65536  Metric:1
      RX packets:16 errors:0 dropped:0 overruns:0 frame:0
      TX packets:16 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:0 
      RX bytes:1184 (1.1 KB)  TX bytes:1184 (1.1 KB)

/var/lib/NetworkManager/NetworkManager.state**:

[main]
NetworkingEnabled=true
WirelessEnabled=true
WWANEnabled=true
WimaxEnabled=true

/etc/NetworkManager/NetworkManager.conf**:

[main]
plugins=ifupdown,keyfile,ofono
dns=dnsmasq

[ifupdown]
managed=false

/etc/udev/rules.d/70-persistent-net.rules**:

# This file was automatically generated by the  /lib/udev/write_net_rules
# program, run by the persistent-net-generator.rules rules file.
#
# You can modify it, as long as you keep each rule on a single
# line, and change only the value of the NAME= key.

# PCI device 0x8086:0x156f (e1000e)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="18:db:f2:18:38:56", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"

# PCI device 0x8086:0x24f3 (iwlwifi)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="e4:a7:a0:d8:69:4f", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="wlan*", NAME="wlan0"