TT#185000 Wrong sample rate for asterisk greating messages

Partially reverted commit 7f59aedb4 because it will scale the
asterisk voicemail greating messages rate to 16kHz where asterisk
supports only 8kHz.

Change-Id: I90ad14fc2ae37a9baf168a61e5454b285432fee9

lib/NGCP/Panel/Utils/Subscriber.pm

@@ -2377,7 +2377,7 @@ sub convert_voicemailgreeting{
     #    die('Wrong mime-type '.$mime_type.' for the voicemail greeting. Must be a audio file in the "wav" format');
     #    return;
     #}
-    my @cmd = ( $filepath, '-e', 'gsm', '-b', '16', '-r', '16000', '-c', '1', $filepath_converted);
+    my @cmd = ( $filepath, '-e', 'gsm', '-b', '16', '-r', '8000', '-c', '1', $filepath_converted);
     my $output = '';
     $c->log->debug("cmd=".join(" ", 'sox', @cmd));
     eval {