ssh/tailssh: use control server time instead of local time

This takes advantage of existing functionality in ipn/ipnlocal to adjust
the local clock based on periodic time signals from the control server.
This way, when checking things like SSHRule expirations, calculations are
protected incorrectly set local clocks.

Fixes tailscale/corp#15796

Signed-off-by: Percy Wegmann <percy@tailscale.com>

ssh/tailssh/tailssh.go

@@ -109,6 +109,9 @@ func init() {
 			lb:             lb,
 			logf:           logf,
 			tailscaledPath: tsd,
+			timeNow: func() time.Time {
+				return lb.ControlNow(time.Now())
+			},
 		}
 
 		return srv, nil