Add optional user Fast SER preference for SEL Fast Message Protocol

* Also cleanup description of remaining preferences

See Bug 10719

Change-Id: I81faba77d8b88b24c65156f5139067233869154b
Reviewed-on: https://code.wireshark.org/review/5416
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>