selftests/vsock: add check_result() for pass/fail counting

selftests/vsock: add check_result() for pass/fail counting

Add check_result() function to reuse logic for incrementing the
pass/fail counters. This function will get used by different callers as
we add different types of tests in future patches (namely, namespace and
non-namespace tests will be called at different places, and re-use this
function).

Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://patch.msgid.link/20251108-vsock-selftests-fixes-and-improvements-v4-7-d5e8d6c87289@meta.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>