Remove mbuf_jumbo_alloc and let large mbuf zones use the new uma default contig allocator (a copy of mbuf_jumbo_alloc). Tag other zones which require contiguous objects, even if they don't use the new default contig allocator, so that uma knows about their constraints. Reviewed by: jeff, markj Sponsored by: Dell EMC Isilon Differential Revision: https://reviews.freebsd.org/D23238