servicemp3: start HTTP timeout timer only once

HTTP timeout timer (m_streamingsrc_timeout) is always started when
souphttpsrc element requests creation of streaming thread by
GST_STREAM_STATUS_TYPE_CREATE type of GST_MESSAGE_STREAM_STATUS message.
This timer is only stopped and not triggered when we reach PLAYING state
in HTTP_TIMEOUT limit.

Problem is, that this message can be emitted multiple times (HLS streams)
If this happens when the timer is already stopped (we are in PLAYING state),
then the timer is started again and is triggered, which creates EOF event.

To fix this we start the timer only once, when the message is recieved
first time (in READY state)