Steps to reproduce:

1) Download attached project 'MobileParticlesAdditiveWithFog - NewUnity.zip' and open in Unity
2) Open scene 'MobileParticleAdditiveWithFog'
3) Make sure the Fog is enabled in the Lighting settings (Window >> Lighting)
Observe the Scene view and you will see that transparent part of the Plane with Mobile/Particles/Additive shader is affected by the Fog

Expected result: Transparent part of the Mobile/Particles/Additive shader should not be affected by the global Fog (check attached image 'expected.png')
Actual result: Transparent part of the Mobile/Particles/Additive shader is affected by the global Fog (check attached image 'actual.png')

Reproduced with:
5.4.6f1, 5.5.4p3, 5.6.3p1, 2017.1.0p5, 2017.2.0b8, 2017.3.0a5

Note: Particles/Additive shader is not affected by the global Fog