samples: bpf: add skb->field examples and tests

- modify sockex1 example to count number of bytes in outgoing packets
- modify sockex2 example to count number of bytes and packets per flow
- add 4 stress tests that exercise 'skb->field' code path of verifier

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

samples/bpf/sockex1_kern.c

@@ -1,5 +1,6 @@
 #include <uapi/linux/bpf.h>
 #include <uapi/linux/if_ether.h>
+#include <uapi/linux/if_packet.h>
 #include <uapi/linux/ip.h>
 #include "bpf_helpers.h"
 
@@ -11,14 +12,17 @@ struct bpf_map_def SEC("maps") my_map = {
 };
 
 SEC("socket1")
-int bpf_prog1(struct sk_buff *skb)
+int bpf_prog1(struct __sk_buff *skb)
 {
 	int index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol));
 	long *value;
 
+	if (skb->pkt_type != PACKET_OUTGOING)
+		return 0;
+
 	value = bpf_map_lookup_elem(&my_map, &index);
 	if (value)
-		__sync_fetch_and_add(value, 1);
+		__sync_fetch_and_add(value, skb->len);
 
 	return 0;
 }