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>
And move a couple other types down into leafier packages.
Now cmd/tailscale doesn't bring in netlink, magicsock, wgengine, etc.
Fixes#1181
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>