VT: DSCP implementation.

[Problem] dscp value needs to be updated based on operator's
  requirement. but there is no interface to update the dscp value.

[Solution] Implement interface to set dscp value into socket by
  setsockopt(). dscp value will be taking care by upper layer.

Bug: 142345921

Merged-in: I1468a08f64b71db0f12d96b393263b520109be6d
Change-Id: I1468a08f64b71db0f12d96b393263b520109be6d
Signed-off-by: JainishKumar Anghan <jai.anghan@samsung.com>