perl-scripts: suppress smartmatch experimental warning

smartmatch was introduced with perl 5.10 and was marked
as experimental in 5.14

Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>

html/cgi-bin/firewall.cgi

@@ -23,6 +23,7 @@ use strict;
 use Sort::Naturally;
 use utf8;
 use feature 'unicode_strings';
+use experimental 'smartmatch';
 
 no warnings 'uninitialized';