Fix info --resources for wwan devices

[skatsaounis]

This PR recursively expands the device directory path of sys/class/net devices by appending /device until the it finds a device regular file as a child.

This is needed for devices like wwan which include sub-devices and they differ from typical sys/class/net devices. For such kind of devices, the net info is present at the top ./device directory but rest information needed to fill Card struct is located at ./device/device.

Please take a look below for more info:

# ll --time-style='+' /sys/class/net/wwan0/device/
total 0
drwxr-xr-x 7 root root    0  ./
drwxr-xr-x 3 root root    0  ../
lrwxrwxrwx 1 root root    0  device -> ../../../0000:08:00.0/
-r--r--r-- 1 root root 4096  index
drwxr-xr-x 3 root root    0  net/
drwxr-xr-x 2 root root    0  power/
lrwxrwxrwx 1 root root    0  subsystem -> ../../../../../../class/wwan/
-rw-r--r-- 1 root root 4096  uevent
drwxr-xr-x 3 root root    0  wwan0at0/
drwxr-xr-x 3 root root    0  wwan0at1/
drwxr-xr-x 3 root root    0  wwan0mbim0/

# ll --time-style='+' /sys/class/net/wwan0/device/device/
...
-r--r--r--  1 root root 4096  device
...
lrwxrwxrwx  1 root root    0  driver -> ../../../../bus/pci/drivers/iosm/
...
-rw-r--r--  1 root root 4096  numa_node
...
-r--r--r--  1 root root 4096  vendor
...

Fixes #12153

[tomponline]

@skatsaounis did you want a review of this? If so please can you mark it as ready for review. Thanks :)

[skatsaounis]

@tomponline PR is ready for review. Please take a look :)

[skatsaounis]

Before change:

$ lxc info --resources
Error: Failed to retrieve network information: Failed to add device information for "/sys/class/net/wwan0/device": Failed to read "/sys/class/net/wwan0/device/device": read /sys/class/net/wwan0/device/device: is a directory

After the change:

$ lxc info --resources
...
NICs:
...
  Card 1:
    NUMA node: 0
    Vendor: Intel Corporation (8086)
    PCI address: 0000:08:00.0
    Driver: iosm (6.2.0-33-generic)
...

[tomponline]

Please can you update the PR description with what has changed in this PR so I can understand and review. Thanks

[skatsaounis]

Comments and descriptions have been added

[tomponline]

Thanks!