decproxy2: set active-mode when doing trick-play
decproxy2: set active-mode when doing trick-play

Decproxy set active-mode to TRUE on fakeadec, then fakeadec is going to drop
all of the buffer and send GAP event instead of buffer.

Change-Id: I56d3f1dfb5602e4d08f819d3c8470278390f1e54
Reviewed-on: https://gpro.lgsvl.com/77999
Tested-by: Wonchul Lee <9841bdbec9dbb2acc2dcaaa1dab0491399f0e464@lge.com>
Reviewed-by: HoonHee Lee <41497318ef67053f37c2ac0e974a3369f66d66ec@lge.com>
Reviewed-by: Myoungsun Lee <ef5eccacceb504b4a99b43e8045acc257d388079@lge.com>
Reviewed-by: Wonchul Lee <9841bdbec9dbb2acc2dcaaa1dab0491399f0e464@lge.com>

justinjoy/gst-plugins-cool,justinjoy/gst-plugins-cool