RTSP: Do not close a rtsp socket before rtsp:teardown sent.

[Problem] Rtp packets are keep coming to DUT even
  after MediaPlayer stopped. it was spending network data
  usage even user closed the streaming.
[Cause] A rtsp socket closed before DUT sends rtsp:teardown.
  so that, rtp sesesion were alive till end of the stream.
[Solution] Prevent closing a socket before sending
  rtsp:teardown.

Bug: 193115006

Merged-in: I0190c20f0add446fcb4acac315bcb189381d5807
Change-Id: I0190c20f0add446fcb4acac315bcb189381d5807
Signed-off-by: Byeongjo Park <bjo.park@samsung.com>