Release the state limit of media_streamer_node_add()

Release the state limit of media_streamer_node_add()

Previously, media_streamer_node_add() returns the invalid
state error when the media streamer state is not IDLE.

This condition is now released to let the user can create
a new node and link the node even if the media streamer
state is PLAYING. For example, it is possible to do these
things inside of decoded ready callback directly.

[Version] 0.1.70
[Issue Type] Improvement

Change-Id: I7188abbbf0fd303304b011425790a954033c193f
Signed-off-by: Sangchul Lee <sc11.lee@samsung.com>