libpcp: dont clear NOTIFY_SOCKET after initial READY notification
libpcp: dont clear NOTIFY_SOCKET after initial READY notification

Don't clear $NOTIFY_SOCKET after the initial READY notification,
since it's still needed later for the STOPPING notification.

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp