samples/bpf: fix broken cgroup socket testing

Currently, executing test_cgrp2_sock2 fails due to wrong section
header. This 'cgroup/sock1' style section is previously used at
'samples/bpf_load' (deprecated) BPF loader. Because this style isn't
supported in libbpf, this commit fixes this problem by correcting the
section header.

    $ sudo ./test_cgrp2_sock2.sh
    libbpf: prog 'bpf_prog1': missing BPF prog type, check ELF section name 'cgroup/sock1'
    libbpf: prog 'bpf_prog1': failed to load: -22
    libbpf: failed to load object './sock_flags_kern.o'
    ERROR: loading BPF object file failed

In addition, this BPF program filters ping packets by comparing whether
the socket type uses SOCK_RAW. However, after the ICMP socket[1] was
developed, ping sends ICMP packets using SOCK_DGRAM. Therefore, in this
commit, the packet filtering is changed to use SOCK_DGRAM instead of
SOCK_RAW.

    $ strace --trace socket ping -6 -c1 -w1 ::1
    socket(AF_INET6, SOCK_DGRAM, IPPROTO_ICMPV6) = 3

[1]: https://lwn.net/Articles/422330/Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Link: https://lore.kernel.org/r/20230115071613.125791-5-danieltimlee@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

samples/bpf/sock_flags_kern.c

@@ -5,7 +5,7 @@
 #include <uapi/linux/in6.h>
 #include <bpf/bpf_helpers.h>
 
-SEC("cgroup/sock1")
+SEC("cgroup/sock")
 int bpf_prog1(struct bpf_sock *sk)
 {
 	char fmt[] = "socket: family %d type %d protocol %d\n";
@@ -17,29 +17,29 @@ int bpf_prog1(struct bpf_sock *sk)
 	bpf_trace_printk(fmt, sizeof(fmt), sk->family, sk->type, sk->protocol);
 	bpf_trace_printk(fmt2, sizeof(fmt2), uid, gid);
 
-	/* block PF_INET6, SOCK_RAW, IPPROTO_ICMPV6 sockets
+	/* block PF_INET6, SOCK_DGRAM, IPPROTO_ICMPV6 sockets
 	 * ie., make ping6 fail
 	 */
 	if (sk->family == PF_INET6 &&
-	    sk->type == SOCK_RAW   &&
+	    sk->type == SOCK_DGRAM   &&
 	    sk->protocol == IPPROTO_ICMPV6)
 		return 0;
 
 	return 1;
 }
 
-SEC("cgroup/sock2")
+SEC("cgroup/sock")
 int bpf_prog2(struct bpf_sock *sk)
 {
 	char fmt[] = "socket: family %d type %d protocol %d\n";
 
 	bpf_trace_printk(fmt, sizeof(fmt), sk->family, sk->type, sk->protocol);
 
-	/* block PF_INET, SOCK_RAW, IPPROTO_ICMP sockets
+	/* block PF_INET, SOCK_DGRAM, IPPROTO_ICMP sockets
 	 * ie., make ping fail
 	 */
 	if (sk->family == PF_INET &&
-	    sk->type == SOCK_RAW  &&
+	    sk->type == SOCK_DGRAM  &&
 	    sk->protocol == IPPROTO_ICMP)
 		return 0;