This adds two new lists, one for domains with fasttimo and one for domains with slowtimo. This eliminates the immediate branch/atomics in pffasttimo and pfslowtimo as well as reduces the number of domains/protocols that need to be iterated over each time.
I suspect pf_proto_{,un}register might need to enter the net epoch, but I'm less certain.
I may squash this with D25459 prior to commit.