bpf, cgroup: fix multiple kernel-doc warnings #24326

Job	Run time
set-matrix	1m 17s
build for x86_64 with gcc	4m 37s
build for x86_64 with llvm-16	4m 20s
build for aarch64 with gcc	5m 27s
build for s390x with gcc	13m 58s
veristat	2m 32s
test_progs on x86_64 with gcc	4m 29s
test_progs_parallel on x86_64 with gcc	2m 51s
test_progs_no_alu32 on x86_64 with gcc	3m 37s
test_progs_no_alu32_parallel on x86_64 with gcc	2m 35s
test_maps on x86_64 with gcc	2m 44s
test_verifier on x86_64 with gcc	2m 4s
test_progs on x86_64 with llvm-16	4m 43s
test_progs_parallel on x86_64 with llvm-16	3m 13s
test_progs_no_alu32 on x86_64 with llvm-16	3m 6s
test_progs_no_alu32_parallel on x86_64 with llvm-16	2m 16s
test_maps on x86_64 with llvm-16	2m 39s
test_verifier on x86_64 with llvm-16	1m 41s
test_progs on aarch64 with gcc	4m 58s
test_progs_parallel on aarch64 with gcc	3m 35s
test_progs_no_alu32 on aarch64 with gcc	5m 7s
test_progs_no_alu32_parallel on aarch64 with gcc	3m 15s
test_maps on aarch64 with gcc	3m 35s
test_verifier on aarch64 with gcc	1m 43s
test_progs on s390x with gcc	4m 46s
test_progs_no_alu32 on s390x with gcc	5m 59s
test_maps on s390x with gcc	6m 27s
test_verifier on s390x with gcc	2m 59s
	1h 50m 33s

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