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>
The control plane is currently still eating it.
Updates #1713
Change-Id: I66a0698599d6794ab1302f9585bf29e38553c884
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>