icmp: randomize the global rate limiter

[ Upstream commit b38e7819cae946e2edf869e604af1e65a5d241c5 ]

Keyu Man reported that the ICMP rate limiter could be used
by attackers to get useful signal. Details will be provided
in an upcoming academic publication.

Our solution is to add some noise, so that the attackers
no longer can get help from the predictable token bucket limiter.

Fixes: 4cdf507d ("icmp: add a global rate limitation")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Keyu Man <kman001@ucr.edu>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Change-Id: I8accf5cc9b30c902989816ff7f81a2f359cc686f
Git-commit: d6c552505c0d1719dda42b4af2def0618bd7bf54
Git-repo: https://android.googlesource.com/kernel/msm


Signed-off-by: urevanth <urevanth@codeaurora.org>