This updates all source files to use a new standard header for copyright
and license declaration. Notably, copyright no longer includes a date,
and we now use the standard SPDX-License-Identifier header.
This commit was done almost entirely mechanically with perl, and then
some minimal manual fixes.
Updates #6865
Signed-off-by: Will Norris <will@tailscale.com>
So things like #5660 don't happen in the future.
Change-Id: I01234f241e297d5b7bdd18da1bb3cc5420ad2225
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>