ipn/ipn{local,server}: remove ResetForClientDisconnect in favor of SetCurrentUser(nil)

There’s (*LocalBackend).ResetForClientDisconnect, and there’s also (*LocalBackend).resetForProfileChangeLockedOnEntry.
Both methods essentially did the same thing but in slightly different ways. For example, resetForProfileChangeLockedOnEntry didn’t reset the control client until (*LocalBackend).Start() was called at the very end and didn’t reset the keyExpired flag, while ResetForClientDisconnect didn’t reinitialize TKA.

Since SetCurrentUser can be called with a nil argument to reset the currently connected user and internally calls resetForProfileChangeLockedOnEntry, we can remove ResetForClientDisconnect and let SetCurrentUser and resetForProfileChangeLockedOnEntry handle it.

Updates #14823

Signed-off-by: Nick Khyl <nickk@tailscale.com>

ipn/ipnserver/server.go

@@ -434,7 +434,7 @@ func (s *Server) addActiveHTTPRequest(req *http.Request, actor ipnauth.Actor) (o
 				s.logf("client disconnected; staying alive in server mode")
 			} else {
 				s.logf("client disconnected; stopping server")
-				lb.ResetForClientDisconnect()
+				lb.SetCurrentUser(nil)
 			}
 		}