VT: Corrects RTP/NTP timestamps of RTCP:SR(Sender Report).

[Problem] The time delay from the camera to RTP packetization
  could not be expressed in RTP and RTCP.

[Cause] RTP and NTP timestamp in RTCP sender report
  should represent a current time but it was showing a
  last packet's time.

[Solution] updates RTP and NTP timestamps of RTCP:SR(Sender report)
  based on the time when a RTCP:SR is packetizing.
  So that, receiver can calculate how much time delayed of a
  sender side's in between camera and RTP packetization by
  comparing following timestamps.
 1) RTP, NTP timestamp of RTCP:SR packet.
 2) RTP timstamp of RTP packet.

Bug: 183578712

Signed-off-by: Byeongjo Park <bjo.park@samsung.com>
Change-Id: I81f05093f9124888dd3ac3c343d3e68b3db789f6