[MEDIUM] remove stream_sock_update_data()

[MEDIUM] remove stream_sock_update_data()

Two new functions are used instead : buffer_check_{shutr,shutw}.
It is indeed more adequate to check for new closures only when the
buffer reports them.

Several remaining unclosed connections were detected after a test,
even before this patch, so a bug remains. To reproduce, try the
following during 30 seconds :

  inject30l4 -n 20000 -l -t 1000 -P 10 -o 4 -u 100 -s 100 -G 127.0.0.1:8000/