selftests/xsk: generate simpler packets with variable length

Implement support for generating pkts with variable length. Before
this patch, they were all 64 bytes, exception for some packets of zero
length and some that were too large. This feature will be used to test
multi-buffer support for which large packets are needed.

The packets are also made simpler, just a valid Ethernet header
followed by a sequence number. This so that it will become easier to
implement packet generation when each packet consists of multiple
fragments. There is also a maintenance burden associated with carrying
all this code for generating proper UDP/IP packets, especially since
they are not needed.
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/r/20230516103109.3066-3-magnus.karlsson@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/xskxceiver.h

@@ -35,17 +35,8 @@
 #define MAX_SOCKETS 2
 #define MAX_TEST_NAME_SIZE 32
 #define MAX_TEARDOWN_ITER 10
-#define PKT_HDR_SIZE (sizeof(struct ethhdr) + sizeof(struct iphdr) + \
-			sizeof(struct udphdr))
-#define MIN_ETH_PKT_SIZE 64
-#define ETH_FCS_SIZE 4
-#define MIN_PKT_SIZE (MIN_ETH_PKT_SIZE - ETH_FCS_SIZE)
-#define PKT_SIZE (MIN_PKT_SIZE)
-#define IP_PKT_SIZE (PKT_SIZE - sizeof(struct ethhdr))
-#define IP_PKT_VER 0x4
-#define IP_PKT_TOS 0x9
-#define UDP_PKT_SIZE (IP_PKT_SIZE - sizeof(struct iphdr))
-#define UDP_PKT_DATA_SIZE (UDP_PKT_SIZE - sizeof(struct udphdr))
+#define PKT_HDR_SIZE (sizeof(struct ethhdr) + 2) /* Just to align the data in the packet */
+#define MIN_PKT_SIZE 64
 #define USLEEP_MAX 10000
 #define SOCK_RECONF_CTR 10
 #define BATCH_SIZE 64
@@ -148,11 +139,7 @@ struct ifobject {
 	struct bpf_program *xdp_prog;
 	enum test_mode mode;
 	int ifindex;
-	u32 dst_ip;
-	u32 src_ip;
 	u32 bind_flags;
-	u16 src_port;
-	u16 dst_port;
 	bool tx_on;
 	bool rx_on;
 	bool use_poll;