samples/bpf: xdp1 and xdp2 reduce XDPBUFSIZE to 60

Default samples/pktgen scripts send 60 byte packets as hardware adds
4-bytes FCS checksum, which fulfils minimum Ethernet 64 bytes frame
size.

XDP layer will not necessary have access to the 4-bytes FCS checksum.

This leads to bpf_xdp_load_bytes() failing as it tries to copy 64-bytes
from an XDP packet that only have 60-bytes available.

Fixes: 7722517422 ("samples/bpf: fixup some tools to be able to support xdp multibuffer")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://lore.kernel.org/bpf/168545704139.2996228.2516528552939485216.stgit@firesoul

samples/bpf/xdp1_kern.c

@@ -39,7 +39,7 @@ static int parse_ipv6(void *data, u64 nh_off, void *data_end)
 	return ip6h->nexthdr;
 }
 
-#define XDPBUFSIZE	64
+#define XDPBUFSIZE	60
 SEC("xdp.frags")
 int xdp_prog1(struct xdp_md *ctx)
 {

samples/bpf/xdp2_kern.c

@@ -55,7 +55,7 @@ static int parse_ipv6(void *data, u64 nh_off, void *data_end)
 	return ip6h->nexthdr;
 }
 
-#define XDPBUFSIZE	64
+#define XDPBUFSIZE	60
 SEC("xdp.frags")
 int xdp_prog1(struct xdp_md *ctx)
 {