Patch to allow us to specify an alternate tcpdump binary when running tests.

This patch should be sent upstream.

--- tcpdump-4.7.4/tests/TESTonce.orig	2016-11-22 07:54:46.080609871 +0000

+++ tcpdump-4.7.4/tests/TESTonce	2016-11-22 09:51:15.439509866 +0000

@@ -1,5 +1,7 @@

 #!/usr/bin/env perl

+$TCPDUMP = "../tcpdump" if (!($TCPDUMP = $ENV{TCPDUMP_BIN}));

+

 system("mkdir -p NEW DIFF");

 if(@ARGV != 4) {

@@ -21,7 +23,7 @@

 else {

     # we used to do this as a nice pipeline, but the problem is that $r fails to

     # to be set properly if the tcpdump core dumps.

-    $r = system "../tcpdump 2>/dev/null -n -r $input $options >NEW/$output";

+    $r = system "$TCPDUMP 2>/dev/null -n -r $input $options >NEW/$output";

     if($r == 0x100) {

         # this means tcpdump exited with code 1.

         open(OUTPUT, ">>"."NEW/$output") || die "fail to open $output\n";