net: Use umd_cleanup_helper()

bpfilter_umh_cleanup() is the same function as umd_cleanup_helper().
Drop the redundant function.

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230526112104.1044686-1-jarkko@kernel.org