Just because we don't have known endpoints for a peer does not mean that
the peer should become unreachable. If we know the peers key, it should
be able to call us, then we can talk back via whatever path it called us
on. First step - don't drop the packet in this context.
Updates tailscale/corp#19106
Signed-off-by: James Tucker <james@tailscale.com>
In prep for incremental netmap update plumbing (#1909), make peerMap
also keyed by NodeID, as all the netmap node mutations passed around
later will be keyed by NodeID.
In the process, also:
* add envknob.InDevMode, as a signal that we can panic more aggressively
in unexpected cases.
* pull two moderately large blocks of code in Conn.SetNetworkMap out
into their own methods
* convert a few more sets from maps to set.Set
Updates #1909
Change-Id: I7acdd64452ba58e9d554140ee7a8760f9043f961
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
