riscv, bpf: Increase the maximum number of iterations

Now that BPF programs can be up to 1M instructions, it is not uncommon
that a program requires more than the current 16 iterations to
converge.

Bump it to 32, which is enough for selftests/bpf, and test_bpf.ko.

Signed-off-by: Björn Töpel <bjorn@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20211028161057.520552-2-bjorn@kernel.org