Read SWWAF_IPV6_GROUP_PREFIX, SWWAF_MAX_TRACKED_CLIENTS and SWWAF_LOG_LEVEL (closes #112)

The IPv6 group that is one client, the size of the table of clients and
the level of the process's own lines become settings. clientGroup reads
the group length from them, so limits, bans, history, lookups, AbuseIPDB
scores and per-client anomaly counters all follow it; ratelimit.New
takes the table size; the process logger takes the level once the
settings are read, and request lines, written apart from it, are never
held back.

Judgement call: SWWAF_IPV6_GROUP_PREFIX accepts 32 to 128, the issue's example range.
Judgement call: the log level test picks a free port by listening and closing, since at warn no starting line gives the address.

Model: opus-5-5

internal/proxy/ratelimits_test.go

@@ -72,6 +72,49 @@ func TestRateLimitRefusesBeforeTheApp(t *testing.T) {
 	}
 }
 
+func TestIPv6GroupPrefixSetsTheClientTheLimitsCount(t *testing.T) {
+	t.Parallel()
+
+	// With SWWAF_IPV6_GROUP_PREFIX at 48, the first two addresses, in two
+	// /64s of one /48, are one client, and the second's request breaks the
+	// limit; the third, in the next /48, is another client.
+	const (
+		first  = "2001:db8:9::1"
+		second = "2001:db8:9:1::1"
+		other  = "2001:db8:a::1"
+	)
+
+	for _, tc := range []struct {
+		setting, value string
+		// status and action are those of the request that breaks the
+		// limit: a rate limit refuses it, a byte limit passes it on.
+		status int
+		action string
+	}{
+		{rateLimitPerMinute, "1", http.StatusForbidden, requestlog.ActionRateLimited},
+		{bytesLimitPerMinute, byteLimit, http.StatusOK, requestlog.ActionForward},
+	} {
+		t.Run(tc.setting, func(t *testing.T) {
+			t.Parallel()
+
+			s, _ := startWithAnswers(t, map[string]string{
+				ipv6GroupPrefix: "48", tc.setting: tc.value,
+			})
+
+			s.get(first, http.StatusOK, requestlog.ActionForward)
+
+			line := s.get(second, tc.status, tc.action)
+			if line.ClientGroup != "2001:db8:9::/48" ||
+				line.Offence != requestlog.OffenceLimit {
+				t.Errorf("log line has client_group %q and offence %q, "+
+					"want 2001:db8:9::/48 and limit", line.ClientGroup, line.Offence)
+			}
+
+			s.get(other, http.StatusOK, requestlog.ActionForward)
+		})
+	}
+}
+
 func TestRateLimitExemptPathsAreNeitherCountedNorRefused(t *testing.T) {
 	t.Parallel()