What to do about it?

Regardless of whether kernel bugs are getting worse...
...it would be nice to have fewer of them

More testing needed
By users!
Wider testing of -rc releases would help greatly

Better bug tracking
A single kernel bug database
Actually putting bugs into the database

Better bug fixing
Fixing kernel bugs can be hard work
No access to affected hardware
Unable to reproduce
Developer discipline can be lacking
Known bugs often remain unfixed