Avoid unnecessary call when sampling=1 (#313)

Call to "bpf_get_prandom_u32() % sampling" not necessary when sampling
is 1

bpf/flows.c

@@ -45,7 +45,7 @@
 static inline int flow_monitor(struct __sk_buff *skb, u8 direction) {
     filter_action action = ACCEPT;
     // If sampling is defined, will only parse 1 out of "sampling" flows
-    if (sampling != 0 && (bpf_get_prandom_u32() % sampling) != 0) {
+    if (sampling > 1 && (bpf_get_prandom_u32() % sampling) != 0) {
         return TC_ACT_OK;
     }