bpf: expand section tests for test_section_names

Add cgroup/recvmsg{4,6} to test_section_names as well. Test run output:

  # ./test_section_names
  libbpf: failed to guess program type based on ELF section name 'InvAliD'
  libbpf: supported section(type) names are: [...]
  libbpf: failed to guess attach type based on ELF section name 'InvAliD'
  libbpf: attachable section(type) names are: [...]
  libbpf: failed to guess program type based on ELF section name 'cgroup'
  libbpf: supported section(type) names are: [...]
  libbpf: failed to guess attach type based on ELF section name 'cgroup'
  libbpf: attachable section(type) names are: [...]
  Summary: 38 PASSED, 0 FAILED

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>