[SRU trusty] LP#1359670: Unsigned modules are wrongly tainted and trace events disabled

[Andy Whitcroft]

When we run an out of tree module this taints the kernel (which is fine) it
taints it in such a way that we cannot trace within it (which is not ok).
This makes Ubuntu a poor platform for driver testing and development.
In v3.15 upstream modified the taint flag for unsigned modules to allow
tracing to work against those modules.  Following this email is a simple
cherry-pick of this change.

Proposing for SRU to trusty.

-apw