Compiling the kernel with clang has shown this warning:

net/netfilter/xt_rateest.c:69:16: warning: self-comparison always results in a constant value
                        ret &= pps2 == pps2;
                                    ^
Looking at the code:
if (info->flags & XT_RATEEST_MATCH_BPS)
			ret &= bps1 == bps2;
		if (info->flags & XT_RATEEST_MATCH_PPS)
			ret &= pps2 == pps2;

Judging from the MATCH_BPS case it seems to be a typo, with the intention of comparing pps1 with pps2.

If my intepretation is correct, then the following patch should fix this:

diff --git a/net/netfilter/xt_rateest.c b/net/netfilter/xt_rateest.c
index 220a1d5..4fc6a91 100644
--- a/net/netfilter/xt_rateest.c
+++ b/net/netfilter/xt_rateest.c
@@ -66,7 +66,7 @@ xt_rateest_mt(const struct sk_buff *skb, const struct xt_match_param *par)
                if (info->flags & XT_RATEEST_MATCH_BPS)
                        ret &= bps1 == bps2;
                if (info->flags & XT_RATEEST_MATCH_PPS)
-                       ret &= pps2 == pps2;
+                       ret &= pps1 == pps2;
                break;
        }