Fix modeline (use Wireshark standard with C comment and no C++ comment)

Fix also some indent (tab->4spaces)

Change-Id: Ieef26591d405c6abe622f9fa26d2a7117af3c259
Reviewed-on: https://code.wireshark.org/review/3548
Reviewed-by: Anders Broman <a.broman58@gmail.com>