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/netexternal.cgi

@@ -20,6 +20,7 @@
 ###############################################################################
 
 use strict;
+use experimental 'smartmatch';
 
 # enable only the following on debugging purpose
 #use warnings;