Unity3D's quality settings have a drop-down for "Anisotropic Filtering", and one of those settings is "Forced On". But what level of anisotropy does it force to?
Experimentation tells me that it forces to 8x. If your texture is already set to use anisotropic filtering at a level above 8x, it will remain at that level rather than being downgraded.
This was tested with Unity 5.6.2p4.