Divide by zero in TCP congestion control Algorithm.

Divide by zero in TCP congestion control Algorithm.

Orabug: 16020656
Bug-db: 14798
CVE: CVE-2012-4565
The TCP Illinois congestion control algorithm does not correctly handle a
zero number of RTTs when reading TCP stats, leading to a divide-by-zero
and kernel panic. A remote attacker could potentially use this flaw to
cause a remote denial of service.

Cc: Petr Matousek <pmatouse@redhat.com>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Chuck Anderson <chuck.anderson@oracle.com>
Reviewed-by: Guangyu Sun <guangyu.sun@oracle.com>