udp: remove useless loop in the block callback
udp: remove useless loop in the block callback

In case of spurious wake-up, the function will return NULL. This is OK.

shyamalschandra/vlc,vlc-mirror/vlc,xkfz007/vlc,xkfz007/vlc,vlc-mirror/vlc,xkfz007/vlc,krichter722/vlc,vlc-mirror/vlc,krichter722/vlc,krichter722/vlc,shyamalschandra/vlc,shyamalschandra/vlc,vlc-mirror/vlc,shyamalschandra/vlc,xkfz007/vlc,shyamalschandra/vlc,krichter722/vlc,krichter722/vlc,shyamalschandra/vlc,shyamalschandra/vlc,krichter722/vlc,xkfz007/vlc,xkfz007/vlc,vlc-mirror/vlc,xkfz007/vlc,krichter722/vlc,vlc-mirror/vlc,vlc-mirror/vlc