samples/bpf: fix broken cgroup socket testing

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.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>