selftests/bpf: Fix error reporting from sock_fields programs

selftests/bpf: Fix error reporting from sock_fields programs

The helper macro that records an error in BPF programs that exercise sock
fields access has been inadvertently broken by adaptation work that
happened in commit b18c1f0aa477 ("bpf: selftest: Adapt sock_fields test to
use skel and global variables").

BPF_NOEXIST flag cannot be used to update BPF_MAP_TYPE_ARRAY. The operation
always fails with -EEXIST, which in turn means the error never gets
recorded, and the checks for errors always pass.

Revert the change in update flags.

Fixes: b18c1f0aa477 ("bpf: selftest: Adapt sock_fields test to use skel and global variables")
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20220317113920.1068535-2-jakub@cloudflare.com