[SELINUX]: increment flow cache genid

[SELINUX]: increment flow cache genid

Currently, old flow cache entries remain valid even after
a reload of SELinux policy.

This patch increments the flow cache generation id
on policy (re)loads so that flow cache entries are
revalidated as needed.

Thanks to Herbet Xu for pointing this out. See:
http://marc.theaimsgroup.com/?l=linux-netdev&m=116841378704536&w=2

There's also a general issue as well as a solution proposed
by David Miller for when flow_cache_genid wraps. I might be
submitting a separate patch for that later.

I request that this be applied to 2.6.20 since it's
a security relevant fix.

Signed-off-by: Venkat Yekkirala <vyekkirala@TrustedCS.com>
Signed-off-by: David S. Miller <davem@davemloft.net>