el init script: ensure TABLE is set by default

Otherwise we might end up with empty "$TABLE", while we're
trying to execute:

  echo "del $TABLE" > /proc/rtpengine/control

This will fail with `echo: write error: Invalid argument` error then.

Instead set TABLE by default to '0'. Users can
customize this via /etc/sysconfig/rtpengine,
and the file is sourced after we set the default.

Closes #696

Change-Id: I2f9bb810757507bcc01509ce02676af0d711f515

el/rtpengine.init

@@ -19,6 +19,9 @@
 # Source function library.
 . /etc/rc.d/init.d/functions
 
+# defaults
+TABLE=0
+
 if [ -f /etc/sysconfig/rtpengine ]
 then
         . /etc/sysconfig/rtpengine