canopen: Improve NMT error control and SYNC message dissection

1.  Also show Reserved/Toggle bit of NMT error control

  In case of the node guarding protocol this bit is used as a toggle bit.
  In case of the hearbeat protocol this bit is reserved.

  Reference: CiA 301 (rev 4.2.0), Chap. 7.2.8.3.2

2. Show optional 'counter' parameter of SYNC messages if available

  Reference: CiA 301 (rev 4.2.0), Chap. 7.2.5.3.1

Change-Id: I5dc0ab65e95fec4846a9c8bd8972ef2eba664ee2
Reviewed-on: https://code.wireshark.org/review/5484
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Petri-Dish: Anders Broman <a.broman58@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>