don't create a map before calling bus_dmamem_alloc() (such maps were
leaked). It is believed that the extra destroy of the map was generally
harmless since bus_dmamem_alloc() often uses special maps for which
bus_dmamap_destroy() is a no-op (e.g. on x86).
Reviewed by: scottl
to this event, adding if_var.h to files that do need it. Also, include
all includes that now are included due to implicit pollution via if_var.h
Sponsored by: Netflix
Sponsored by: Nginx, Inc.
