test: temporary increase Hubble buffer size to 64k

Temporary increase the Hubble buffer size in order to capture more
flows. This will hopefully help us understand why the
K8sEgressGatewayTest is occasionally failing (#18012)

Signed-off-by: Gilberto Bertin <gilberto@isovalent.com>

test/helpers/kubectl.go

@@ -92,6 +92,7 @@ var (
 		"hubble.relay.image.repository": "k8s1:5000/cilium/hubble-relay",
 		"hubble.relay.image.tag":        "latest",
 		"hubble.relay.image.useDigest":  "false",
+		"hubble.eventBufferCapacity":    "65535",
 		"debug.enabled":                 "true",
 		"k8s.requireIPv4PodCIDR":        "true",
 		"pprof.enabled":                 "true",