Update copyrights

This patch updates the copyright notifications in the headers of files.
The following patches added by Midokura should use the same copyright
statement as follow:

  Copyright (C) 2014 Midokura SARL.

Signed-off-by: Taku Fukushima <tfukushima@midokura.com>
Merge pull request #7 from tfukushima/copyright-fix

Update copyrights