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 goal here is to
1. make it so that the number doesn't diverge between the various places
we had it defined
2. not define the number in corp, only in oss
Signed-off-by: Maisem Ali <maisem@tailscale.com>
