Alex, 

I tested the patches with the following setup. Please note I tested
the microphone mute led by GUI, as the hotkey does not work on this
system.

Thank you for taking the time to test this series, it is appreciated.  I
would not expect the switching method (GUI/hotkey) to matter here, as
long as we can compare behavior of two kernel versions by consistently
using one of them.

1. Downloaded the below patches from patchwork

9518737 Awaiting Upstream [v2,1/6] dell-led: remove GUID check from
dell_micmute_led_set()
9518761 Awaiting Upstream [v2,2/6] ALSA: hda - use
dell_micmute_led_set() instead of dell_app_wmi_led_set()
9518741 Awaiting Upstream [v2,3/6] ALSA: hda - rename
dell_led_set_func to dell_micmute_led_set_func
9518725 Awaiting Upstream [v2,4/6] platform/x86: dell-laptop: import
dell_micmute_led_set() from drivers/leds/dell-led.c
9518727 Awaiting Upstream [v2,5/6] dell-led: remove code related to mic mute LED
9518735 Awaiting Upstream [v2,6/6] dell-led: move driver to
drivers/platform/x86/dell-wmi-led.c
9520053 Awaiting Upstream [v2,6+/6] platform/x86: dell-wmi-led: fix
coding style issues

2. Installed Ubuntu 16.10 (Linux kernel 4.8) on Dell Latitude 7180

Just to be sure, I assume you meant 7280?

  -> Microphone mute led works as expected

3. Applied downloaded patches to kernel 4.8 without any conflicts, but
kernel will not compile successfully.

I am confused.  This patch series should apply cleanly to 4.9 and its
surroundings.  Between 4.8 and 4.9, commit 4875a5f72180 ("ALSA: hda -
Fix a failure of micmute led when having multi adcs") happened.   This
makes it impossible to apply this patch series cleanly on top of 4.8
without reducing context to one line.

Moreover, I applied this patch series (with reduced context) to 4.8 and
successfully compiled the kernel.  Could you shed some light on where
exactly did your build crash?

4. Installed Ubuntu Zesty kernel (Linux kernel 4.9)

  -> Microphone mute led works as expected

5. Applied and compiled downloaded patches to kernel 4.9

  -> Microphone mute led does not work

Any chance of a git bisect?

6. Compiled and installed Linux kernel 4.10 rc8

  -> Microphone mute led does not work

This is even more confusing.  Between 4.9, which you claim works fine,
and 4.10-rc8, which you claim does not work, I can see no changes to
either drivers/leds/dell-led.c or sound/pci/hda/dell_wmi_helper.c.
Kernel configuration issue?

7. Applied and compiled downloaded patches to kernel 4.10 rc8

  -> Microphone mute led does not work

No surprises here if it really does not work with 4.10-rc8.

-- 
Best regards,
Michał Kępień