contrib/check-config: check for xt_bpf
We omit xt_u32 as it's optional; since we will remove support for this
module in the future, it's simpler to check for xt_bpf, which will
become the new baseline.
Related issues:
* https://github.com/microsoft/WSL/issues/10029#issuecomment-1574440255
* https://github.com/docker/for-win/issues/13450#issuecomment-1574443139
Signed-off-by: Bjorn Neergaard <bjorn.neergaard@docker.com>
Bjorn Neergaard