Real goal is to eliminate some allocs in the STUN path, but that requires
work in the standard library.
See comments in #2783.
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This lets a trusted DERP client that knows a pre-shared key subscribe
to the connection list. Upon subscribing, they get the current set
of connected public keys, and then all changes over time.
This lets a set of DERP server peers within a region all stay connected to
each other and know which clients are connected to which nodes.
Updates #388
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Brad Fitzpatrick