remove duplicated code to start the server threads, use

remove duplicated code to start the server threads, use
the infrastructure exposed in http.c earlier today.

As a bonus, now we can restart the session on a different
port just reloading the module.

On passing, fix a bug in the handling of 'enabled' in the configuration
file - previously, a missing "enabled=" line in manager.conf meant
"whatever the state was before" instead of a specific value.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@48338 65c4cc65-6c06-0410-ace0-fbb531ad65f3