Close correctly AVFormatContext in socket-manager.c.
Close correctly AVFormatContext in socket-manager.c.

Now we close the AVIOContext associated to the AVFormatContext
with avio_close function.
With this we fix the problem to left the UDP ports opened.

Kurento/kc-media-native,shelsonjava/kc-media-native,javiaf/kas-media-native,javiaf/kas-media-native,Kurento/kc-media-native,javiaf/kas-media-native,shelsonjava/kc-media-native