mbufs and mbuf clusters are now backed by large pools. Because of this

mbufs and mbuf clusters are now backed by large pools. Because of this
we can relax the oversubscribe limit of socketbuffers a fair bit.
Instead of maxing out as sb_max * 1.125 or 2 * sb_hiwat the maximum is
increased to 8 * sb_hiwat -- which seems to be a good compromise between
memory waste and better socket buffer usage.
OK deraadt@