Eliminate proto_tree_add_text from packet-sna.c.

Also convert many of the proto_tree_add_boolean calls into proto_tree_add_bitmask.

Change-Id: I1fb2f943abed28434a2aadc48eb7e9ffb766f463
Reviewed-on: https://code.wireshark.org/review/5523
Reviewed-by: Michael Mann <mmann78@netscape.net>
Petri-Dish: Michael Mann <mmann78@netscape.net>
Reviewed-by: Anders Broman <a.broman58@gmail.com>