selftests/bpf: Fix s390 sock_field test failure #21414

Job	Run time
set-matrix	1s
build for x86_64 with gcc	4m 35s
build for x86_64 with llvm-16	5m 8s
build for aarch64 with gcc	5m 11s
build for aarch64 with llvm-16	5m 10s
build for s390x with gcc	15m 15s
veristat	2m 53s
test_progs on x86_64 with gcc	5m 14s
test_progs_parallel on x86_64 with gcc	3m 56s
test_progs_no_alu32 on x86_64 with gcc	4m 33s
test_progs_no_alu32_parallel on x86_64 with gcc	3m 34s
test_maps on x86_64 with gcc	3m 43s
test_verifier on x86_64 with gcc	2m 40s
test_progs on x86_64 with llvm-16	4m 40s
test_progs_parallel on x86_64 with llvm-16	3m 46s
test_progs_no_alu32 on x86_64 with llvm-16	4m 3s
test_progs_no_alu32_parallel on x86_64 with llvm-16	3m 5s
test_maps on x86_64 with llvm-16	3m 45s
test_verifier on x86_64 with llvm-16	2m 11s
test_progs on aarch64 with gcc	5m 55s
test_progs_parallel on aarch64 with gcc	3m 51s
test_progs_no_alu32 on aarch64 with gcc	5m 17s
test_progs_no_alu32_parallel on aarch64 with gcc	3m 47s
test_maps on aarch64 with gcc	4m 8s
test_verifier on aarch64 with gcc	2m 39s
test_progs on aarch64 with llvm-16	6m 6s
test_progs_parallel on aarch64 with llvm-16	3m 57s
test_progs_no_alu32 on aarch64 with llvm-16	5m 18s
test_progs_no_alu32_parallel on aarch64 with llvm-16	3m 40s
test_maps on aarch64 with llvm-16	4m 9s
test_verifier on aarch64 with llvm-16	2m 35s
test_progs on s390x with gcc	19m 29s
test_progs_no_alu32 on s390x with gcc	16m 56s
test_maps on s390x with gcc	54m 18s
test_verifier on s390x with gcc	6m 50s
	3h 52m 18s

Provide feedback