Max silence was represented in milliseconds, yet vmminsecs (minmessage) was represented
as seconds.

Also, the inequality was reversed. The warning, if triggered, was "Max silence should 
be less than minmessage or you may get empty messages", which should have been logged 
if max silence was greater than minmessage, but the check was for less than.

Also, conforming if statement to coding guidelines.

closes issue #15331)
Reported by: markd

Review: https://reviewboard.asterisk.org/r/293/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@203721 65c4cc65-6c06-0410-ace0-fbb531ad65f3