libbpf: Prevent overriding errno when logging errors

libbpf: Prevent overriding errno when logging errors

[ Upstream commit 23ab656be263813acc3c20623757d3cd1496d9e1 ]

Turns out there were a few more instances where libbpf didn't save the
errno before writing an error message, causing errno to be overridden by
the printf() return and the error disappearing if logging is enabled.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200813142905.160381-1-toke@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>