libbpf: Delay feature gate check until object prepare time

libbpf: Delay feature gate check until object prepare time

Commit 728ff167910e ("libbpf: Add gating for arena globals relocation feature")
adds a feature gate check that loads a map and BPF program to
test the running kernel supports large direct offsets for LDIMM64
instructions. This check is currently used to calculate arena symbol
offsets during bpf_object__collect_relos, itself called by
bpf_object_open.

However, the program calling bpf_object_open may not have the permissions to
load maps and programs. This is the case with the BPF selftests, where
bpftool is invoked at compilation time during skeleton generation. This
causes errors as the feature gate unexpectedly fails with -EPERM.

Avoid this by moving all the use of the FEAT_LDIMM64_FULL_RANGE_OFF feature gate
to BPF object preparation time instead.

Fixes: 728ff167910e ("libbpf: Add gating for arena globals relocation feature")
Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260217204345.548648-3-emil@etsalapatis.com