[ Upstream commit c5fa5d602221362f8341ecd9e32d83194abf5bd9 ]

The return value for each test in test_libbpf.sh is compared with

    if (( $? == 0 )) ; then ...

This works well with bash, but not with dash, that /bin/sh is aliased to
on some systems (such as Ubuntu).

Let's replace this comparison by something that works on both shells.
Signed-off-by: NQuentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NSasha Levin <sashal@kernel.org>