selftests/bpf: Simplify the calculation of variables

Fix the following coccicheck warnings:

./tools/testing/selftests/bpf/test_sockmap.c:735:35-37: WARNING !A || A
&& B is equivalent to !A || B.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/1614757930-17197-1-git-send-email-jiapeng.chong@linux.alibaba.com