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>
This ensures that each DERP server is probed individually (TLS and STUN)
and also manages per-region mesh probing. Actual probing code has been
copied from cmd/derpprobe.
Signed-off-by: Anton Tolchanov <anton@tailscale.com>
Will Norris