Fixes a problem with RTCP PLI packets not being sent. The problem was that the usePLI field of VideoMediaStreamImpl was accessed from the constructor of the superclass (through the overloaded deviceSessionChanged method), before being initialized. As a result it's value was 'false' rather than the intended 'true'. This patch makes the field static, since (once initialized) it's value was always 'true' anyway.

This is the stack trace observed:
     [java] 	at org.jitsi.impl.neomedia.VideoMediaStreamImpl.deviceSessionChanged(VideoMediaStreamImpl.java:520)
     [java] 	at org.jitsi.impl.neomedia.MediaStreamImpl.setDevice(MediaStreamImpl.java:1678)
     [java] 	at org.jitsi.impl.neomedia.MediaStreamImpl.<init>(MediaStreamImpl.java:284)
     [java] 	at org.jitsi.impl.neomedia.VideoMediaStreamImpl.<init>(VideoMediaStreamImpl.java:318)
     [java] 	at org.jitsi.impl.neomedia.MediaServiceImpl.createMediaStream(MediaServiceImpl.java:364)


git-svn-id: https://svn.java.net/svn/jitsi~svn/libjitsi@10620 198c5059-ef06-4ec0-9a75-fdd6b0ef00a6