Maybe like this?

#!/usr/bin/perl
use strict;
use warnings;

open PO, "netstat -na|" or die "Can't pipe open: $!\n";
  my %count;
  while (<PO>) {
    next unless /^udp/ or /^tcp/;
    my @fields = split;    # split $_ on whitespace
    $count{$fields[3]}++;
    ## next jumps here
  }
close PO;

for my $ip (sort keys %count) {
  print "\t$count{$ip} $ip\n";
}
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