sys: Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

Regularize the Netflix copyright

Use recent best practices for Copyright form at the top of
the license:
1. Remove all the All Rights Reserved clauses on our stuff. Where we
piggybacked others, use a separate line to make things clear.
2. Use "Netflix, Inc." everywhere.
3. Use a single line for the copyright for grep friendliness.
4. Use date ranges in all places for our stuff.

Approved by: Netflix Legal (who gave me the form), adrian@ (pmc files)

Add a kernel test framework. The callout_test is a demonstration and will only
work with the upcoming async-drain functionality. Tests can be added
to the tests directory and then the framework can be used to launch
those tests.

MFC after: 1 month
Sponsored by: Netflix Inc.
Differential Revision: https://reviews.freebsd.org/D1755