Add checkfiltername.pl to pre-commit script

Change-Id: I34d8aa7034a4aacc2a95b35a30f25356b33a51b9
Reviewed-on: https://code.wireshark.org/review/5187
Reviewed-by: Michael Mann <mmann78@netscape.net>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>