Destroy session first, and destroy group later

Destroy session first, and destroy group later

Description: In wfd_destroy_group, memory of peers which are member of
group is freed. In wfd_destroy_session, the peer is need to check
whether a session is completed or not. So, if we use wfd_destroy_group
first, wfd_destroy_session couldn't be used.

Change-Id: Ied2e68a18c829b5ea36e86191888116ac86f5da0
Signed-off-by: Yu jiung <jiung.yu@samsung.com>