wgengine/monitor: ignore OS-specific uninteresting interfaces

Currently we ignore these interfaces in the darwin osMon but then would consider it
interesting when checking if anything had changed.

Signed-off-by: Maisem Ali <maisem@tailscale.com>

wgengine/monitor/monitor_freebsd.go

@@ -34,6 +34,8 @@ func newOSMon(logf logger.Logf, m *Mon) (osMon, error) {
 	return &devdConn{conn}, nil
 }
 
+func (c *devdConn) IsInterestingInterface(iface string) bool { return true }
+
 func (c *devdConn) Close() error {
 	return c.conn.Close()
 }