*Steps to reproduce:*
# Create a Unity project and add a Monobehavior that prints the value of _Screen.dpi_
# Build and run the application on an SDL platform (Linux, EmbeddedLinux, or QNX).
# Check the DPI value of the display.

*Actual results:* 

DPI is 0.

*Expected results:* 

Screen.dpi should be set to the correct dpi value of the display.

*Observations:*
* _SDL_GetDisplayDPI_ returns false and while defaulting dpi values to 0. 
* This bug does not happen on Linux using Wayland.

*Reproducible with versions:* 

Reproduced on Unity 6000.2.0a8 and 6000.3.0a1

*Tested on (OS):* 

EmbeddedLinux (using X11 and Wayland)

Linux (using X11)

Not yet tested on QNX.